After several side-by-side battles, Tsunoda attempted to finally pass the McLaren rookie for seventh place on lap 49 of 71 with the aid of DRS into Turn 1.
But as he moved around the outside, his right-rear wheel tagged Piastri's front left to trigger a spin. He re-joined the track in 16th and finished in 12th.
Although Tsunoda defended his attempted overtake on Piastri, he has now revealed that his frustration was sufficiently "hard to digest" that he shut himself away in his Mexico City hotel room.
Facing the media ahead of the Brazilian GP this weekend, he said: "I was really frustrated after the race because I lost the opportunity to score points for the team.
"I was having a good race until then. So, I really had massive frustration and actually, it was hard to digest that frustration on that day.
"Normally, Mexico, you can enjoy. I actually cancelled everything and just stayed in the room. It was a big moment, and it was an opportunity… P5 was definitely possible."
Tsunoda added that he "tried to be patient as much as possible" when passing the McLaren and that it was "easy" to be alongside Piastri given the overspeed he had with DRS at the end of the main straight.
But he recognised that he should have taken extra caution and used more "situation management" given it was a fight for points - as AlphaTauri tries to bank extra prize money by passing Williams for seventh place in the constructors' championship.
Asked by Motorsport.com to explain his coping mechanism, Tsunoda continued: "I feel first of all guilty.
"I don't know whether it's a conscious thing or whatever, but I just feel pretty bad if I play around and have a distraction after I have a bad race.
"Maybe it's good, but it will be just for me. It will be just temporary. I thought about everything - what I can improve in the future.
"It was obviously tough, but it gives me time to rethink. For me, it's the thing I normally do if I have a bad race. I only have a party if I have a good race."
Tsunoda had previously talked about learning from experienced team-mate Daniel Ricciardo to improve his "emotional control". He reckoned this was something he had so far "never achieved, especially the last grand prix".
