Doxylamine
"I took 1(one) 25mg tablet. I haven't been sleeping well so thought I would try this. I did fall asleep within about 30 minutes. I awoke about 6 hours later and my room was literally spinning. I was so dizzy feeling I could barely get to the bathroom and then back to bed. I fell back to sleep quickly which for me is unusual. I slept for another 3-4 hours. When I awoke I was still quite dizzy feeling but not like when I had woke up previously. That was 5 days ago. I have had dizziness since I took that one  pill and have not taken any more. I must be extremely sensitive to this medication. I have also had some nausea this whole time."