The Window of Tolerance is a idea developed by Dan Siegal. He suggested we all have 3 key states.

There is the optimum layer, where you are able to exert self control and everything is manageable. This is the like the middle layer of a sandwich.

The top of the sandwich is where you are very hyped up, buzzing, out of control. The lower layer is where you feel zoned out, withdrawn maybe numb.

If you have a large optimum layer you cope better in life and do not easily zoom into the over stimulated layer or fall through into the zoned out layer.

This podcast explains the WOT in detail and ways of increasing your optimum layer.