Constantly tired 3year old & mood change?

My son is 3years old, his normally a happy playful child, argues to go to bed like any child. His bed time is 7.30 but wont drift off til about 8-8.30pm. He has 12hour sleeps so he will wake about the same time in the morning give or take. Usally he plays til about 10.30-11am & then he is tired again usally he will sit on the lounge & just fall sleep for 2 or so hours then wake up play again & try to go back to sleep. This hasnt happened before so when it started to occur it caught me by suprise. His mood towards me has changed his tone of voice is alot more aggressive towards me & before asking him to pick up his toys was no problem now he will come up & punch me & tell me no. I dont wanna go to the doctors just as yet as i have monitored his behaviour & sleep pattern for the past 3 days but if anyone has experienced this before & could lead me into the right direction with it would much be appreciated. Ive also noticed when he gets tired he gets extremly large & black circles under his eyes it almost looks like someone has hit him