Well, do you mean you just said the last thing in the conversation or did you say something like a question or continuing of the conversation she should have replied back to? If the latter, wait a bit. If the former, I don't see a reason to wait, as long as you're casual about it and just send one message. But even if it's the latter, you said she fell asleep so that's probably why she didn't answer. A casual message today wouldn't hurt.
I'm with Simon. I think the
way you go about this is more important than any specific rules or anything. But also, yeah don't send 80 messages lol. Sending one noncommital message probably looks more nonchalant than waiting. You know, don't act like it's a big deal and worry about making the wrong move (aside from no repetitive messages of course) and you'll come off better.
Quote from: sneakersjay on April 08, 2013, 09:58:08 AM
At least wait until she responds, but DO NOT reply immediately as if you were waiting to send the second you got her message.
This too. I think being cool and casual about it means not immediately replying, and also not waiting too long between replies which can make it seem like a bigger deal. So, a balance there. You don't want her thinking you're waiting on purpose or that you're not interested.
Quote from: sneakersjay on April 08, 2013, 09:58:08 AM
I would wait, too. I used to be one who sent messages (not texts) and was guilty of too many too soon. I didn't perceive them as being excessive (and it truly wasn't overboard). But after I was on the receiving end of too many messages/texts (in the same quantity and vein that I myself was guilty of!) I found it was truly off-putting and people came across as needy or desperate and that made them unattractive. Keep busy, think of her, but I would definitely wait before sending her another message. At least wait until she responds, but DO NOT reply immediately as if you were waiting to send the second you got her message. I ruined countless (haha I rarely dated) potential relationships because of it.
If you really like her, show some restraint. 
Jay
This sounds like me after I've been a total jerk and offended the person. A zillion 'sorry, I didn't mean it' pleas.

Took a long time for me to realize that approach doesn't work.