We carry a nylon lunch bag everywhere we go, royal blue with purple trim, containing two plastic syringes, each preloaded with 5 mg of liquid Valium, plus packets of surgical lubricant and plastic gloves. At the first sign of blinking or twitching, we lay him on his left side, tug down the elastic waist of his pants, part his small buttocks, and insert the gooped-up tip. Within moments, the motion stops, as if an engine has been switched off. Then he falls into a deep sleep. When he relaxes, so do we.

He's 5 years old, the first time. Our babysitter takes him to a pizza place for lunch. He laughs mid-slice, blinks his eyes several times, slumps to the floor, and climbs back onto his chair. She hesitates — what was that? — and then calls 911. She pages me. I keep the message stored in my beeper, periodically daring myself to relive my first reading of it.

I meet them in the ER at the community hospital near our home, showily flashing my downtown hospital ID tag. Soon my husband rushes in, wearing the ID from his downtown hospital. All the tests are negative, they say. Bring him back if something else happens.

Something else happens. The next day, I skip work and keep him home from school. He sits happily in front of cartoons while I pace and polish, pace and fold. Maybe the babysitter overreacted, I reason. Maybe he's just a goofy kid. The moment I stop watching him, he cries, “Look, Mommy! Look what my hand can do!”

Downtown. No mistaking it this time. Grand mal, big and bad, right on the gurney. Lumbar puncture. MRI. All negative. Before we go home, the neurologist asks if we have further questions. “Just one,” I say. “What do we do if he does it again?” The neurologist seems surprised. His raised eyebrows silently ask, “Aren't you both doctors?” He hands us a pamphlet.

Dilantin. Chewable yellow triangles three times a day. Triangles to first grade and the beach and day camp and a sleepover. The other kid has cochlear implants. “Don't worry,” his mother says, accepting my baggie of pills. “My kid comes with instructions, too.” We become members of an exclusive club no one wants to join.

One day, almost exactly a year later, the school nurse calls. “It's been 10 minutes and it's not stopping,” she says. I'm home that day and I screech over in seconds, leaving one tire on the schoolyard curb. He's in the nurse's office, lying on the plastic divan reserved for kids with sore throats, bellyaches. Fakers. I know what this is called, this shaking that will not stop. I know how to treat this, in adults. But all I know now is how to hold him, jerking, foaming, soaked with urine.

In the ambulance, the foam turns bloody. I ask the ponytailed EMT whether he will die. She pretends not to hear, turns to adjust his oxygen. At the local ER, I bark instructions. “He has a neurologist downtown,” I say. “He needs to be transferred.” The ER attending, who has been bending over him with her lights and sticks, straightens. “I think,” she says, not unkindly, “Mom needs to wait outside.”

Tubed, taped, lined. Ready for transfer. There is one last thing. The ponytailed EMT hands me a specimen cup in which the source of the blood that had burst my heart open rattles. “Here, Mom,” she says, smiling. “For the tooth fairy.”

Back at home, 40 pills a day, crushed, on spoons of Breyers cookies-and-cream ice cream. Still he blinks and shakes, shakes and drops. The weeks go by like a slow and sickening descent, landing on the carpeted floor of the playroom in our basement. We spend most of the day there because it's the only place in the house where he can't fall down the stairs. At night we tuck him tightly into Star Wars sheets but still find him on the floor in wet pajamas. If the Valium fails, we call 911. A fire truck arrives with the ambulance, and the firefighters, with their giant boots and helmets, crowd along with the EMTs into the small bedroom our boys share, delighting our younger son.

He is admitted. He is discharged. He is admitted and discharged again. Admitted. Discharged. Admitted. Discharged. Admitteddischargedadmitteddischargedadmitteddischargedadmit-teddischarged. My husband, too tall for the fold-out-chair bed, takes the day shift. I pad in slippers through the hospital at night with the other parents. We buy one another coffee. We commiserate. I grow more at ease in this sleepless company than with anyone else — my family, my friends, my medical colleagues. I also cling to the nurses, Jen and Sarah and Kristen and “the other Jen,” as we call her. One leaves my son's chart in his room, and I sneak a look. “Mom at bedside,” a progress note reads. “Appears calm.”

Finally, a break. The sixth or seventh MRI shows a subtle irregularity in the right temporal lobe, possibly a tiny tumor, a focus. We love the very word “focus,” a raft of hope in a vague and endless sea of anxiety. Never have parents been so happy to learn their child might have a brain tumor.

The surgery works. The medications are discontinued. I don't ask to read the pathology report, the operative note. I am startled by my lack of medical curiosity. I wish to know nothing other than that my son no longer shakes. After the staples come out, we pile into the car and take a 9-hour drive — unthinkable during the previous months — to visit my in-laws. On the way home, my husband glances at the back seat through the rearview mirror and, returning his eyes to the road, says, “He's blinking again.”

A second surgery. A third. This time, we're lucky. “The luckiest unlucky parents ever,” I joke.

Years pass. We renovate our kitchen and find the lunch bag with two dried-up syringes of Valium in a cabinet about to be torn down. Our emaciated boy doubles in weight and then doubles again. He graduates from high school. He graduates from college. He moves away from home.

I do not know how much he remembers. He rarely speaks of those years, except to comment on whether a barber has done a good or not-so-good job of hiding the scars.

As for me, occasionally my terror will snap to life again, as if I've been holding it by a long and slack tether. It happens when I am walking through the peaceful, leafy streets of our town, pumping my arms, working my aging heart and muscles, quieting my busy mind. A siren sounds. An ambulance appears. Though I know from reading the log in our local paper that the emergency is rarely dire — a dog bite, an asthma attack — and I know that my son is nowhere near, I still stop to see which way the ambulance is heading.

People ask, “Is it easier or harder to have a sick child when both parents are doctors?” But this is the wrong question. There is no hard, no easy. Only fear and love, panic and relief, shaking and not shaking.