I remember the exact moment when I realised my therapist could not stop death. I had just watched a man die – my boyfriend’s step-father, the first death I’d ever seen up close – and it became achingly clear to me that I, too, would one day face the dying process. It wasn’t that I was previously unaware of my own inevitable death. I’d talked about it, written about it, and joked about it as much as any respectable poet should, which is to say, a lot. When I wasn’t pontificating glibly about taking the big dirt nap, I’d been greatly haunted by the reality of my own demise – particularly when coming down off psychedelics or following an all-nighter on speed.

Yet in those other instances, it was as though I had a choice as to whether or not to look death in the face. Even on drugs, I was always eventually able to pull the curtain down and think about something else. But now it was as if the barrier between me and death-awareness had vanished. There was no curtain left to pull down, no blinder left to put on. I feared that it was finally happening: the bats in my belfry had at last taken over and I would be trapped permanently in this state.

Seated on my therapist’s avocado-green replica of a midcentury modern sofa, I told her about my existential terror. She replied to me using words meant to soothe, but I do not recall what she said. All I could hear were my own thoughts: my therapist cannot change the fact that I’m going to die. She can’t even change the fact that she is going to die. Compared with death, my therapist is just a crappy pound-shop hairbrush.

In that moment, I felt a great loneliness. I tried to pacify myself with the idea that every human being faces death eventually. But who cared what those other people would be doing? My death was mine, and mine alone. There remained a whole layer of my being that no one, not even my therapist, could touch.

I’ve found it easiest to be honest about myself when I am anonymous, disembodied, not sitting across from another human being. About six years ago, I started an anonymous Twitter account called @SoSadToday, because I was going through a cycle of anxiety and depression that therapy, medication and everything else I’d used to treat it in the past, weren’t working. What began as a small gesture of tweeting into the void in a dark corner of the internet has now amassed more than half a million followers. In many ways, I feel more connected to them than I have ever felt with a therapist. We all come from different backgrounds, but there is a universality of feeling among us. While the account is no longer anonymous, I still pretend it is. It’s as though I have my hands over my eyes and am playing the game of “If I can’t see you, then you can’t see me.”

People often ask me if I am always sad or if @sosadtoday is a character. I’d say that, in totality, I’m not always sad. But I’d also say the account is not a character or a persona either. Rather, @SoSadToday reflects one part of me – the part that I have difficulty showing others, including therapists, in my daily life.

After 18 years of therapy I decided to take a break this year to see if I would be OK on my own, and digest some of what I’ve learned. Prior to this hiatus, I’ve seen a range of different therapists and, while some were more effective than others, I’ve always felt there were parts of me that were untouchable to all of them. In many ways, this has been my own doing as I’ve gone to great lengths to avoid being fully seen. As an alcoholic in my early 20s, I would go to therapy drunk so as to assuage the tremors and rapid heartbeat that came with facing another individual sober. If my therapist knew I was steeped in alcohol, she never let on. Nor did I ever discuss my drinking problem with her. We would talk about my mother, sex, physical anxiety. Sometimes I would even have vodka-enhanced revelations, or “breakthroughs”. But these were built on shifting sand.

So what was the point of even going to therapy if I couldn’t be honest? Why bother sitting in her office drunk when I could just be at the bar? I continued to go because I did want to get well. I just wanted to get well without giving up alcohol. It was alcohol, I felt, that gave me the courage to go and participate in my own “healing”. I wanted to be OK, but was scared to reveal how deeply I wasn’t.

Wasn’t therapy supposed to be a “safe space”? Why was I having a panic attack there?

After getting sober at 25, I then spent my late 20s and early 30s in New York in psychodynamic therapy, attempting to find relief from the chronic panic attacks that still plagued me. Sometimes I would have a panic attack right in the middle of a session, the perfect opportunity to really take a look at the physical experience with someone who was supposed to understand. And yet, whenever the attack happened during a session, I would say absolutely nothing. I would talk right around it instead.

I told myself the reason for my reluctance to reveal the panic attack was that I didn’t want to hurt the feelings of whichever therapist I was seeing. Wasn’t therapy supposed to be a “safe space”? Why was I having a panic attack there? I didn’t want to make her think she was bad at her job – a therapist who triggers anxiety in people. In truth, I was afraid that if I was having a panic attack in therapy, then there was something incurably fucked-up about me. If I wasn’t OK in a therapist’s office then how could I be OK anywhere else?

So I suffered my shortness of breath, sweating palms and dissociation on my own, all the while bantering about my childhood. I felt much less vulnerable conveying an intellectual understanding of my family history than saying: “Right now, I feel like I’m suffocating.” I preferred to woo a therapist with my sense of humour, self-knowledge and intellect – thus convincing myself that I was at least sane enough to charm.

I’ve had plenty of therapists say: “If you need me you can call me.” But I’ve never taken them up on that. To me, that kind of vulnerability – to really need someone in a time of crisis – felt unsafe. Better not to be the needy patient, a person who is “too much”. Better to call an anonymous hotline instead. At least the voice on the other end had no idea who I was.

It may sound strange to attend therapy, all the while only allowing the therapist into the foyer of my consciousness. But as a person with anxiety disorder, I figured that some therapy was better than no therapy. For all of the discomfort of being misunderstood, there were times when I received great solace and help – in romance and family life – from therapy. What’s more, I couldn’t imagine not being in therapy. As an American, a Jewish woman and a New Yorker, it was just what you did.

I once had a mediocre therapist in New York for seven years, because I was afraid to break up with her. She was a kind old lady, a 1970s abstract artist who provided Jungian analyses of my dreams. But if I tried to discuss my eating disorder, she’d say: “What if you eat a nice hardboiled egg?” Or, if I wanted to explore my body dysmorphia: “Just put calamine lotion on that zit.” I wanted to say: “Listen, it’s not about the zit. It’s about my feelings of self-worth as they are hyper-related to a minor physical flaw.” But I never did, because it seemed easier to just accept the useless advice than confront her. In the end, it took me moving 3,000 miles away to make the final break.

Therapists often use the in-office relationship as a mirror of the way their patients are in the world. They will read deeper meaning into an innocuous action, like when I am 10 minutes late and spend the rest of the session discussing whether the lateness was intentional – if there was something I was avoiding. Sometimes, there was just traffic. But when it comes to a fear of disclosure – of being honest with the person hired for that purpose – I do think it can be a reflection of the patient’s life.

My reluctance to be fully honest with therapists reveals an ingrained expectation of rejection or judgment on a more universal level. My inability to speak up for myself conveys a fear of confrontation, of saying no, of not being liked. It also depicts an innate fear of scarcity – that if I speak up, then I will be cut off and left out in the cold with no one. What’s more, there is a self-centredness in my reluctance to break up with someone who isn’t a good fit. It’s as though I perceive myself as so important to another person that the impact on their life left by my leaving will be devastating.

Maybe, despite the best efforts of psychology, we aren’t ever entirely knowable to ourselves

The therapy modality that has had the most profound effect on my anxiety disorder is a mindfulness-based form of cognitive behavioural therapy called acceptance-commitment therapy. I like the fact that there are worksheets and homework, as though I am merely collecting data on thoughts and their related feelings for analysis.

When I bring in the data to my therapist, I feel a level of detachment – as though we are scientists conducting a study. Together, in the lab, my fellow scientist and I parse which thoughts are true and which are fantasy.

But on a more personal, humanistic level, there is some kind of existential need in me to avoid touching my own unknowableness. It is as though I fear that I, like the whale in Moby-Dick, can never be seen in totality or understood fully. Thus, by only revealing pieces of myself, I preclude facing that vast enormity of the self. At times, I feel that a stranger walking down the street could tell me more about myself in 10 seconds than I could ever really know.

Maybe, despite the best efforts of psychology, we aren’t ever entirely knowable to ourselves. When people ask us how we are, we lie for different reasons. Sometimes we say, “I’m OK,” because it’s just easier. Who wants to be the person that responds: “Well actually, I’ve been staring into the dead centre of a gaping existential hole. Thanks for asking!” Other times we have no idea we’re lying. We say “I’m OK,” because we don’t know that we’re not.

The Pisces by Melissa Broder is published by Bloomsbury at £16.99. Order a copy for £14.44 at guardianbookshop.com