Ahhh....checking....I know it well. Listen there are things you can do to stop this behavior. The first is not to give into the impulse to go back and look. So when you do something, i.e., send the email, take your medication, say out loud "I TOOK MY MEDICATION" or "I SENT THE EMAIL" this way when you have that moment of shear panic, you can remember that you said those words out loud. It happens to me with the iron, the door lock, etc. I say it out loud and then when I panic, I remember what I said and the panic goes away.
What you cannot do is give in. You cannot go back and look. You have to stop yourself because until you say "ENOUGH" you are going to be stuck in this cycle of checking, panic, checking, panic.
Thank you so much JGF25, you give great advice and I am going to try your technique today! I truly appreciate your response; it's such a relief to be able to chat about this issue with people who get it!