寝ようと思う。

to lie down; to go to bed; to lie in bed; to sleep (lying down); to sleep (with someone, i.e. have intercourse); to lie idle

if; when; and; with; particle used for quoting (with speech, thoughts, etc.); quoting particle; promoted pawn; indicates question (sentence end)

to think; to consider; to believe; to think (of doing); to plan (to do); to judge; to assess; to regard; to imagine; to suppose; to dream; to expect; to look forward to; to feel; to desire; to want; to recall; to remember