That step #1 is a huge one. Just accepting the loss and calling it what it is. People get hung up going over what could have been or reliving the bet/game etc. Once its passed let it go and move forward. Assess what you need to do to get by it which the op mentions a few. After a huge loss a cooling down period is probably the best thing. Walk away for a bit.
This should certainly be the case in gambling, because one should only participate in gambling if one has the patience and self-control to afford the amount of loss one can afford. There will be losses/gains in gambling and you have to accept it. Of course, if it causes temporary stress, it would not be bad to share it with close friends. By doing these two things - accepting losses and sharing them with close friends - a gambler will not break down mentally because close friends or relatives will be able to comfort him in those bad moments.