I'm 42 with no known health problems, but is this normal?
I do get up quite early at 5.30 ish because the cats start hassling me and I like to have a coffee before dealing with the morning rush - breakfast for all, etc. DD (12) leaves the house at 7.15, DS (14) at 7.40, DH (46) at some point before 8 and I leave with primary-aged DS at 8am.
Get home at about 8.40 and then run / walk dog for an hour. Then pilates every other day or something like food shopping if not. Sometimes I might stay out all day, but (here is the problem) - if I go home between the hours of say 1-3 before the school run, I know that if I sit down on the sofa for even a minute I will fall asleep. One minute I'm awake, 2 seconds later, I'm out of it, just like that. I will sleep sitting up. This happened today and I almost missed the school run 
The evenings are very busy for me in our house, but if we do sit down to watch GBBO or something, the same thing will happen. I will doze off about 10 mins into the show, even if I really want to watch it. Then later on, if DH and I are watching a Netflix series or something, I always miss the second half so can't keep track of the general plot.
I never used to be like this - has anyone else experienced similar after they hit 40? Does it get worse? Any advice welcome!