'''Did it always act this way?''' What OS are you running, ''The last two releases have had a lot of sleep/wake issues. ''
If you have not changed the OS '''you could have a corrupt .plist file'''.
'''Create a new user account''' and use it just as a test. Does it act the same or as you expected. If the behavior stops you have eliminated a hardware problem. You can go back to your main account and try to track it down ''(deleting a corrupt .plist file is a "fix" for strange application behavior)''.
''If this answer is acceptable '''please remember to return and mark it accepted'''.''