It puts alot of strain on your system and liver especially, my best guess is that your body is trying to heal its self and a side effect of that is being very tired... also hard to eat, never tried it my self but pretty much any one who uses superdrol ( which is funnily enough made from anapolan ) loses all appetite.
I understand the use of orals and strong drugs, but I see no need for me personally to use such strong stuff.
Another thing I notice is some guys feel good on anapolan, and feel crap on dianabol, pretty topsy turby