I remember JKR said something about this in an interview once. I just can't remember when or where it was posted. She did compare it to clinical depression.
Dementors feed on people's happy memories, they sort of 'suck them out' of you. When given a Dementor's kiss, people seem to be totally numb. I'll have to read the boos again to get a more accurate description.
There is nothing in canon that says that a Dementor's kiss can be reversed, but newer magical research could perhaps find a way? (This is pure speculation, I know.)
Yes, I believe the word Dementor could be derived from either word. After all, it has to do with something that affects the mind negatively.