All this fitness is tiring me out

Went the gym last night, and then had to go bed early as i felt like shit - thought that all this keep fit mallarky was supposed to keep you healthy and give you energy - i just had a headache - hopefully there's just a bit of something going around, so i think I will just work through it, going to aqua aerobics tonight,a and then having my program updated at the gym ion the morning - i will be healthy if it kills me!!!