wow that's such a huge question as there are so many answers and at the end of the day everyone is unique. Even two people who have experienced the exact same thing can have different feelings.

Thoughts always preceed feelings, so to try and calm down the feelings that may seem too much for the given situtation, I think you have to challenge the irrational thoughs (like people do in CBT). However sometimes sitting through them and realising that they come and go, can also be helpful.