Yeah, I agree with Sun. When I first started working out (for the first time in 2 years) I felt like I was going to die. My head hurt, my chest felt heavy, I was dizzy and wanted to faint. But that's normal because your body was used to doing nothing and all of a sudden you're telling it to get up and do things!
My advice is to take it slow. Start with a few minutes a day. Like 5 minutes, than add a minute everyday. I've been doing this and am up to 12 minutes and have felt no harsh after effects because you are slowly easing into activity instead of trying to push yourself suddenly. Hope that helps!