Doxylamine
"I am a nurse and struggled with sleep while on night shift. I took half a Doxylamine (Restavit) and slept well.  An hour after waking I then went into fast atrial fibrillation (HR 160 - 200), I ended up in emergency needing D/C Cardio-version to revert me back to a normal rhythm.  Though I have colleagues who have had good results with this medicine I had a terrible experience and will never take it again.  POTENTIALLY a very dangerous drug!!!!  be careful."