What if
Stress is caused as much by what goes on in our heads as goes on around us. Inordinate amounts of time are given over to concerns of the past characterised by the two expressions "what if" and "if only".
We can recreate the stress of past events by simply thinking about them. We do have a choice as to what we want to think about. Learn to let go of past events by first appreciating that whatever we do we cannot change the past. Find a positive lesson to use from the event (there is always one to find) and use it to shape the future.
If you find yourself caught in re-analysing a past event then put in place a pleasant or positive memory like a holiday or an event you have enjoyed. Really work through each part of the happy memory returning to it each time your thoughts turn to the "what if" situation.
Thinking positively in this way is as much like physical exercise: the more you practise the better it gets.