Aussie Bob - ever had a spot you worried was skin cancer, and not just a mole?
You spend so much time, not worrying about the problem, but about what the consequences to a possible problem MAY be, and all of the combinations - keeps you up at night.
One professional, who can look at the spot, and say - this is definitely not cancer because [insert technical reason here]. Or even - this IS cancer because [insert technical reason here] - and THIS is what we can do about it. Takes all that "extra" worry away, and allows you to concentrate on the problem - that reduces the stress from "a thousand things which may go wrong" to just dealing with the issue (if there is one) at hand.
So - with stress, especially incident related stress and Post Traumatic Stress Disorder (PTSD) the same applies. Humans don't react logically - you feel guilty when logic tells you you should feel proud. You giggle when logic tells you you should cry (ever done that at a funeral?), and so on, and so on.
To have a professional, who has spent time examining the reams of studies on this behaviour, simply listen to what you are feeling and worrying about - and then tell you what is "normal" (even when it seems stupid) and what is not is what counselling is about. It allows you to stop worrying about the weird stuff which keeps you up at night (because studies tell you it's normal) and concentrate on the problem. It helps.
It speeds up the "dealing with it" process from the years it took the WW2 boys to months.