
Often times it is not a single thing which causes this, its a plethora of stress elements which dominate your reasons to be content and happy. ( smile is often deceptive so dint mention here ). The sudden anxiety and adrenaline you feel rushing through your veins is what troubles the most. It leaves in a state where you may think more and take steps you may not have taken, if not make you regret.
The only cure to this is take compulsive actions for/against whatever you are thinking. Diverting mind via movies, work or songs doesn’t really work and if it does its ephemeral. You WOULD think of a mango if i ask you NOT to think of one.
Once you do something about it, you will feel lighter if not good and at the same time you now have a reason (your action) to be upset/influenced by the thought. Its human nature to be trapped in this vicious circle of chained reactions and this differentiates us from machines.
Okay enough i can go on with this for forever, time to act though I may not...