Idea's !! They're everywhere

I know my biggest writing problem.. I see ideas everywhere. I want to write a mystery and have one of the characters be Elvis's ghost, I want to write a historical fiction about the pony express and Vinnie Ream and fictional horse books for boys and a romance novel and another romance novel where the girl become the cute boy's boss and .... can someone give advise about stopping the high I get on when I start plotting a new idea... the pounding of my heart as I form words and this idea becomes a living word form... to stop cooing to the new baby and remember the other kids in my doc file.