I made a lot more progress when I had a spotter. Everyone's body reacts differently, but mine seems to relish grinding out one extra rep.
I've only been trapped under a barbell once, but not in the way you would expect.
I was trying to do some improvised seated barbell calf raises (see image below), but due to a combination of having long legs and using a high foot platform to maximise ROM, my knees were a lot higher than my hips and the barbell ended up rolling down my thighs. Due to the angles and balance in the situation, I couldn't stand up and it was digging in pretty hard. I probably could have got it off if I needed to, but I found it hilarious, so asked a guy near me to lend a hand and he came and deadlifted 100kg off me.