Using a verb as a habitual thing vs Chinese
"you think I sleep?" in Chinese should be "你以為我睡觉吗?" 

以為 imply 'mistakenly presume"

The other answers and comments already pointed out the fact that everyone sleep. the sentence "you think I sleep?" need a lot of clarification-- (Why you don't need to sleep? How can you do it?) 

Let's use more logical examples: 

"you think I care?" =  "你以為我在乎吗?"

"you think I lie?" = "你以为我撒谎吗？"

"you think I forgot?" = “你以为我忘了吗？”


if you don't like 以為 (thought/ mistakenly presume), you can use 覺得 (think/ feel) or 认为 (consider/ think). But 以為 is the best choice here because this type of short retort imply whatever idea the other person has is wrong.
吗 can be omitted