I have written things during many drunken stupors-I stored those away and cringe when I read them (notes written on various pieces of paper). Eventually I will throw them away.
I've written during withdrawals to remind me how I felt so I wouldn't do it again ( um...tried to make that work).
As to tell your therapist-never been. How comfortable r you with this person? It really depends on you and your relationship with him/her. Maybe start off slowly and see how it feels for you.
Remember this is your journey-you are in charge. Good luck.