I notice that recently I can't fall asleep at night despite feeling sleepy, and my heart is racing really fast. I think it's because I'm anxious or stressed out.

I exercise in the evenings on my stair climber and do crunches and arm weights. I'm not overweight, in fact I lost 20kgs over a span of a year and been maintaining it fairly well with cutting down my food intake.

So anyway, I'm often very sleepy in the day. What could be causing my heart to race at night? Is it just stress?