hamster sleeping all day and night

[sea the hamster]

i got a hamster a syrian one or golden one and is like 4 months now that i have him. now that this hot days came he became very inactive, he's sleeping all day (ofcourse) but he's sleeping during the afternoon too. I mean before he was so active and he played a lot when 8 o clock came, but now he just stay awake without playing... probably its very hot i dont know what to do... i play with him and when i put it back to his place he just lays there and stabs ... please help me.. he is healthy eats and drinks and no eye irritation or thing like this ((( i am so worried, i dont want him to die thank you !