like badbaggirl said, it's normal to have some depression, espceially since it's only been a little while since you had your surgery and you might still be having some pain and just now getting used to dealing with the mechanics of the bag. Also, since your life wasn't awful before, it may be harder for you.
But you did say you had some down times, there won't be anymore of those! no more meds, no more watching your diet, or wondering where the bathroom is! also, no more drinking that awful stuff for colonoscopies, and you said you had dysplasia, i think that means precancerous cells, and an ostomy, to me, would be much better than havign to go though chemo and all that. Plus, you have a few less areas to worry about getting cancer in, i know that sounds like a weird plus, but to me it is!
My life is back to normal, actually it's back to better than normal! before normal was miserable pain all the time, lots of meds, missing out on things. Now normal is workign without worry, eating what i want, when i want (although i do suggest you do not try pizza anytime soon, lol) going whereever i want, without a thought as to where a barthroom is.
Also, do like badbaggirl said(she gives good advice) and keep posting here and listening to positve stories, and go to support groups. ANd if you need those friends, call them, and tell them, they sound like they must be good friends to have been there for you, just ask them to hang around some.
hope things get better!