I think it is fine to play that way since you are just doing what you can to win points. I don't think I would go as extreme as you did, but that's me. I know my serve slows down as the match progresses, but I do not consciously slow it down ... fatigue does it for me. If I think too much about my serve, that's exactly when it fails me. The mind can do funny things. "Hey I haven't double faulted in this match yet. Ooops."
NTRP 3.5 with < 130mph TTW serve | Head Microgel Radical MP (3g split at 3&9, 5g in handle) | Babolat Xcel French Open 16ga @ 58 | Year 2 of playing