Hey Chris, if you search for 'depression' in this thread you'll find it's there pretty regularly.
I know that I had it at about the time you're in. Matter of fact, the second time, I was ready for it, knew it would be there and was forewarned to ride it out.
I think we not only have to heal physically, but mentally also. None of us is a block of ice. The stress of the decision we've made, the recovery, expectations, inactivity in the beginning and the perceived weakness of being in crutches, etc. are things we're unused to.
Once you begin seeing the positive, really are able to move well, the pain is gone, that lessens, but depression is something many of us run into. The best thing for me was to recognize it, know it is finite and then in the end show it on its way and close the door on the way to better.
Normal to me.