? about sleep stages 3 & 4

I read a post yesterday that talked about sleep stages 3 and 4 but I can't find it today. I think Janelle wrote the response. Anyway, there was discussion about spending enough time in stages 3 & 4 to feel well rested. My question is "how much time is enough time?" I am still very tired even though I'm very compliant so I'm wondering if I'm spending enough time in the appropriate stages of sleep.
Thanks..Amy