眠 (Kanji for sleepy)

Onyomi

MIN	Our 4 year old gets MEAN when he's sleepy.

I'm too sleepy to keep an eye on my folks.

ねむ*い	sleepy from being up all day (BOOBOO: not to be confused with being tired from work or exercise, which is 疲れる) ★★★★☆
ねむ＊る	to sleep ★★★★☆

睡眠(すいみん)

sleep ★★☆☆☆ NP
睡 (sleep) + 眠 (sleepy) = 睡眠 (sleep )

a somewhat medical-sounding word for sleep (BOOBOO: you would never say, "よく睡眠した?" -You gotta say, "よくねた?")

睡眠薬(すいみんやく)

sleeping pill ★☆☆☆☆
睡眠 (sleep ) + 薬 (medicine) = 睡眠薬 (sleeping pill)

不眠症(ふみんしょう)

insomnia ★☆☆☆☆
不 (un) + 眠 (sleepy) + 症 (symptom) = 不眠症 (insomnia )