Simple tiredness isn't really an issue with me. Lately, I've been truly exhausted. Not sleepy, not tired, just completely physically and mentally drained. Sunday, my one day off, I did too much, and paid the price. After working 65 hours, I really shouldn't have gone to the playground for 2 hours then played golf in the hot sun for 4. I got home and was shaking; I literally passed out on the couch at 6:15 and slept until 11. I woke up, and even though I was stripped down to my underwear, no shirt or anything, I was sweating like crazy. And I had the room down to 70 degrees! I drank a liter of water and stumbled upstairs for another 8 hours of deeeeep sleep.
I assume that insomnia is worse than exhaustion, but exhaustion is pretty bad too.