 [ Symptoms ] why do i feel lightheaded fatigued and sweat during sleeping no fever  i am an almost 37 yr old female with a lot of stress right now dr put me on effexor and i started not being able to sleep having bad headaches feeling lightheaded and constipated i took it for 2 weeks and he told me to stop when i called him he called me in something else but i am afraid to get it i have been on paxil prozac and celexa and never felt this horrible i have not taken anything in almost a week but feel lightheaded many times thoughout the day any ideas what could be wrong [ Disease ] i have also experienced this i do not drink much water do you if not i suggest when you feel that way drink a few glasses of water and see how you feel a few hours later it helps me when dehydrated you will feel hot flashes headaches feels like you might pass out but do not almost like your brain clicks off for a second its a weird feeling kinda hard to explain you will sweat at night too drink more water plan and simple