Choke: had plenty of those but the one that still rankles was in a doubles tournament this year. We were up 7-2 in the 10pts match tiebreaker... ended up losing 10-8.
Comeback: a doubles tourney last year. Lost first set 6-1. Came back from 2-5 down in the second to force a tie-breaker, and won it 8-6. Won 10pts match tiebreaker 11-9.
Somehow I never have these wild rides in singles... it's always more orderly, one way or the other