So sorry you're dealing with all this, ImWorried. Yes, medically-related symptoms can be frightening. I know when I'm concerned, I have to try hard to not play the 'what if' game.
Sunny13 has some great suggestions. Also, bravo for taking the bull by the horns and making an appointment for a colonoscopy and upper endoscopy! That 'says' you are trying to stay on top of whatever may be going on. I would guess you'll be relieved once the testing is over. I know I generally feel lots better just getting things checked out.
Maybe in the meantime, spoil yourself a little! Do some things you find enjoyable: A good book, shopping, maybe even splurge on something you've wanted for a while. Watch funny movies. Sometimes it just helps to try to divert your mind and keep busy.
Keeping you in my prayers and wishing you the best. Keep us posted. You can do this!
"Be faithful in small things because it is in them that your strength lies."
Blessed Mother Teresa