I believe that everybody has experienced an unexpected tactical blow over the chessboard. Every game has some tactical motives and grounds for combinations. I strongly believe in a positional approach, i.e. every combination must have some grounds to be performed. Lack of these grounds makes combinations incorrect and leads to worse position.
However, in practical chess we have another factor that affects our play - emotions. A sudden move turns everything upside down, and such a sharp change impairs our judgement.
Here I will not talk about correct combinations, when you simply overlooked an effective move that leads to your defeat. We will talk about "go complex" play.
What are the effects of a tactical hit?
1) it undermines players self-esteem "I overlooked something meaning - I am playing bad"
2) the combination can be possibly incorrect and refuted, but it requires time and effort to find a correct line
3) everyone knows that it is easier to attack than to defend, as defending you need to count all variations exactly to avoid punishment.
4) for the majority of players (even grandmasters) it is psychologically hard to shift from quiet play to defence.
Needless to say that the play "for complications" is very advantageous for sharp tactical players (a good example was Mikhail Tal). Even if their combination is not entirely correct, those players go for it, relying on the psy-effect and their ability to count faster. Usually they win.
What are the remedies?
Firstly, calm down. Blood pressure and heartbeats need to be within the norm Even if it is your move - take a walk. Let the other player gloat a bit. Elation is not a good advisor either.
Second, abstract from emotions and try to understand what happened and why.
Third, try to find the best reply line by looking into ALL, I repeat ALL possible variations. Spend more time if that can potentially save your game.
The main thing is not to make a move, unless you got the whole picture of the situations and the action plan.
The more resilient and experienced player is - the better he/she can handle the situation.
I would like to bring two examples of my recent play. In both games I lost, even though the result could be exactly the opposite.
In the above example thinking just a little bit more would have saved (if not won) the game.
The second example is also very informative
Now look at the above position after the proper line of 1...Kxh7
As we saw, in both games I could have turned the table. The only reason why that hasn't happened is - I should have had a clear head and thought more to find the proper line. So trivial.
Every game as such makes you more experienced and teaches not to stress up even when the situations seems to be hopeless. As one of the chess Commandments I would put "Thou shalt not relax"