What was wrong with him?`

[The Red Rooster]

I had a cockatiel that didn't seem right. He got a little better with taming but there was a point where you ran into a brick wall. He would sleep ALL day! I saw him play with a toy only once. Maybe I was stressing him out? I felt bad for the little fellow so I sold him to some nice bird people.

I think he was stressed out. Poor guy

 

[TwoCrows]

I don't think mental stress would make him sleep all day. Some sort of physical stress such as an illness would make him sleep all day. I have had stressed Cockatiels and they show their mental stress in biting, shaking, nervousness. So yours probably had some illness of some sort. Very young and very old birds will sleep all day. Along with sick birds. Sorry.