Over the last year or so I have found it harder and harder to stay awake all day, especially if I have done any physical exercise. This just seems to be getting worse. This morning I walked for an hour and a half (had plenty of time and didn't fancy getting the bus). It was not a difficult trek! It was on the level and I walk a lot. I had to go to bed for a couple of hours tthis afternoon though to recover. This is getting ridiculous. My doctor says it's normal at my age (not yet 50!) and that my iron levels are slightly low. Is it really normal???