being "tired"

What does it really mean to be tired? I have heard it said that being tired is a state of mind. I agree with that, for the most part :)....and, right now, my state of mind is tired. If you are going on an hour of sleep or just ran a marathon, I would say there is a legitimate reason to be tired. I also know that sometimes a list of things I have to do ringing in my head and not knowing when or how I'm going to do them, can be more exhausting than running a marathon on being on an hour of sleep...although I have not attempted that yet. I do know though, that I have more control over whether or not the first one makes me tired, than I do the second. See, just writing about this and putting it in a different perspective...I'm no longer tired. Now, I'm going to shift it back again, because I need to get some sleep.