On the surface, it might seem like there's not too much of a difference between bipolar disorder and borderline personality disorder. Both mental health disorders can involve mood shifts and problems with impulse control — so much so that even doctors in a clinical setting can sometimes have a difficult time telling the two disorders apart when making an initial diagnosis. Though bipolar disorder involves a series of manic or depressive "mood episodes," while borderline personality disorder is more about an ongoing pattern of behavior, the extreme ups and downs that sufferers of both disorders must deal with can make them look awfully similar from the outside. If you have questions about a loved one's unpredictable moods — or even your own — you might have a hard time figuring out which disorder seems more applicable to your situation.

While they have many similar elements, bipolar disorder and borderline personality disorder are different disorders — and their differences are important. Understanding those differences is most important, of course, in making sure sufferers get the right treatment. Managing bipolar disorders (which include bipolar I & bipolar II, as well as cyclothymic disorder) involves different medications and therapeutic techniques than managing borderline personality disorder, and undergoing psychological treatment for a different mental health condition than the one you have can cause a lot of problems — for instance, antidepressants can actually make some people suffering from bipolar disorder feel worse.

Understanding these differences is important for people who don't suffer from either of the disorders too; it helps us understand how complex mental health is, and how complicated it can be to find and get the right treatment. What someone dealing with a mental health issue seems to be going through is only part of the story, and people who appear to be battling the same symptoms can be dealing with very different problems inside. Knowing this can help us become more understanding, more empathetic, and (perhaps most importantly) more likely to believe people struggling with mental illness when they tell us what it feels like.

1. Each Disorder's Depression Feels Different

We tend to think of depression as a singular experience — our ideas about depression probably involve images of someone who feels physically and emotionally exhausted, who is crippled by self-hatred and blames themselves for problems they didn't create. But this is only one particular way that depression can play out in a person's life — in reality, different mental health disorders cause sufferers to experience extremely different versions of depression.

People dealing with borderline personality disorder and people dealing with bipolar disorder will both sometimes suffer through periods of intense depression. However, the details of each kind of depression are different. According to a 2014 article published in Current Opinion In Psychiatry, "in contrast to 'typical' depressive features (e.g. decreased self-esteem, self-criticism) frequently associated with BP II, BPD depressive states are often more characterized by emptiness, shame and 'painful incoherence'." (As per the article, the "painful incoherence" that many depressed BPD sufferers feel is "emotional pain related to a fragmented sense of self.")

This means that while depressive periods for sufferers of both disorders may involve common elements, like changes to sleeping habits or appetites, they lead to different kinds of feelings. A person dealing with bipolar disorder may spend their depressive episode feeling guilty and thinking about perceived past mistakes, while a person with borderline personality disorder may experience depression as more of an abstract feeling that also includes elements of anger and frustration.

A report published in the Israeli medical journal Harefuah also found "BPD patients reporting higher levels of cognitive and anxiety-related symptoms" than patients with bipolar disorder during depressive periods, further painting a picture of a different kind of depression than what's usually associated with bipolar disorder.

2. BPD Is More Constant Than Bipolar Disorder

BPD and bipolar disorder are so often mistaken for each other because of the way that the two disorders cause a sufferer to shift between moods. But the way the disorders actually play out in the sufferer's life is different. While folks who have bipolar disorder experience depressive and manic or hypomanic episodes, they also experience periods where they are not undergoing any kind of episode, and feel that they are at an emotional "baseline." In contrast, borderline personality disorder doesn't afflict sufferers on an episode-by-episode basis; that disorder's impact on the sufferer's life is more consistent.

As Lecia Bushak wrote in a 2015 piece for Medical Daily:

"Experts note that one of the main differentiating factors between bipolar and borderline personality disorder is that symptoms of personality disorder are pretty consistent and ongoing, while people with bipolar disorder appear to have 'breaks' between their extreme mood swings, in which they experience a mid-range mood where most of the symptoms that are confusing between the two disorders (impulsivity, anger, irritability, extreme emotion) aren’t present."

So while a person with bipolar disorder will likely experience a period of time in which their disorder won't necessarily guide their feelings or daily life, a person with borderline personality disorder feels the impact of their disease most of the time.

3. BPD Has More To Do With Interpersonal Relationships

One of the key differences between these two disorders is the role that other people play in them. Bipolar symptoms can manifest in the total absence of interpersonal interaction; though some mood episodes will be triggered by a stressful or emotionally loaded interaction with another person, mood episodes can also come seemingly out of nowhere — a product of pure biochemistry.

Conversely, borderline personality disorder is a disease that has a lot to do with how the sufferer interacts with others (in addition to how the sufferer views themselves). According to Current Opinion In Psychiatry, "Individuals with BP II are more likely than those with BPD to have autonomous mood episodes and lacking an interpersonal context...By contrast, symptoms of BPD are usually reactive, generally triggered by a psychologically salient interpersonal event such as frustration, rejection or a sense of abandonment." Or, as author Randi Kreger put it in Psychology Today, "The moods in people with BPD are more dependent, either positively or negatively, on what's going on in their life at the moment" than those of people with bipolar disorders. While bipolar disorders are diagnosed by a pattern of mood episodes, borderline personality disorder is diagnosed by a consistent pattern of behavior that involves, according to the National Institute of Mental Health, "A pattern of intense and stormy relationships" and "Extreme reactions—including panic, depression, rage, or frantic actions—to abandonment, whether real or perceived."

How Can I Make Sure I'm Getting The Right Diagnosis?

Obviously, a psychologist who's been through medical school knows more about diagnosing mental illnesses than a random blogger like myself. But if you or a loved one has been diagnosed with one of these disorders, and you feel like something's a bit off — for instance, if you've been diagnosed with a bipolar disorder, but you feel like your mood shifts are always the result of an emotional interaction with another person, don't be afraid to ask for additional testing. You spend every day in your own skin, and you may notice things that your clinician misses. Both bipolar disorders and borderline personality disorder can be difficult to manage, but they both respond well to treatment, if that treatment is correct. So don't be afraid to speak up — and know that, no matter what your diagnosis is, getting it is the first step towards feeling healthy.

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