There are 2 things wrong with this picture...
1) If you are using your computer as a DAW, then it should never been in sleep mode
2) Always shut your program down when your done...

When your computer goes to sleep, it sends out a message to all components connected to it, that it's time to take a nap. Well, all of your components don't have a sleep command written into their instructions, like your Midi Interface, or your Audio interface - so these devices in other words become confused and they can either lose functionality and not play audio or midi, freeze the program or in extreme cases crash the computer completely..

So STAY AWAY FROM SLEEP MODE!!!!!