There are two common reasons for getting stressed out and over-stimulated.

The PCS brain often has a hair trigger fight or flight system. Very minor stressors to most people become major stress events for people with PCS.

Over-stimulation is often a result of the brain losing the ability to ignore or filter out stimulation that would normally be filtered out. This can be due to organic injury or chemical stress that reduces the effectiveness of brain functions. This can cause the fight or flight hair trigger.

If the brain is not getting full stage sleep, toxins can collect decreasing the efficiency of the brain cells.