Tilt

Tilt is any emotional state that makes a player play worse than their own normal standard — usually looser and more aggressive after a loss, though it can also mean playing scared and passive. The decisions are still theirs; what has changed is the judgement behind them.

Most often a bad beat, a long run of losing pots, a needling opponent, or losing a big pot to a player the person thinks is worse than them. Fatigue and playing stakes above your comfort level make all of it more likely.

The reliable answer is leaving the table. Serious players set a stop-loss before they sit down — a number of buy-ins or a time limit — because the decision to quit is much easier to make before you are tilted than during. Short breaks, lowering stakes and reducing the number of tables also help.