I recently had to stop gabapentin (300mg AM, 300 8PM, 300 bedtime), even though it worked well for fibro pain. The problem was probably more due to taking tramadol in the same day, as I know it causes me to have the precursors to serotonin syndrome, muscle spasms, when I take too much (4 a day) or with many other meds.
I was starting to have muscle spasms overnight. One day as I was waking up the muscle spasms started in the left leg, ran up to my abdomen and after a minute or two, paralyzed my diaphragm, making it impossible for me to breathe - fortunately only for a half a minute or so, but it happened two more times! My husband told me I had been having spastic motions of my arms and hands, and my eyes had been going back and forth while I was sleeping. Of course I stopped the gabapentin immediately! Withdrawal cold turkey was horrible, but I was more afraid of not being able to breathe than the pain.
I feel better now off the gabapentin. Can't sleep, though. Looking for something else for that. Wish my only pain reliever that works, tramadol, would last a little longer.
Apnea and muscle spasms are known side effects.