sleepy是形容词,意思是：困倦的,想睡的.做定语和表语asleep是形容词,是意思是"睡着了的"强调状态只做表语(表语形词)sleeping是形容词,意思是：意思是"在睡觉的",强调动作 做定语另外它还是个动名词.sleep是动词,意思是睡觉.sleepy 指人“困倦的或瞌睡的”状态，作表语时，意为“困倦；想睡觉”，作定语时，意为“瞌睡的；寂静的”。

如:She always feels sleepy in class because she stays up late.因为熬夜，她上课总感到困倦。asleep是表语形容词，意为“睡着的”，常用于短语fall asleep,意为“睡着”。如:Don't wake them up. They're asleep. 别吵醒他们，他们睡着了。sleep是动词或名词，意为“睡觉；睡眠”。如:He didn't sleep well before the exam.考试前他没睡好。