The Wheels Keep Turning

When I was a kid my dad used to look at me and say he could "see the wheels turning".  As in, my brain is working overtime and I'm thinking really hard about something.  Those closest to me know the look on my face that signifies I'm deep in thought.  Lately, it seems I have this look all the time.  I can't stop thinking about things, to the point that I know I'm over-analyzing.  I know this is my reaction to fear, sometimes irrational fear, but I still can't seem to stop.  I'm not sleeping very well.  My stomach is upset.  I haven't been this happy in so long and it's like my brain is trying to prepare me for the worst.  Like maybe if I doubt things, when they do fall apart it won't hurt so much.  But is that really possible?  I'm so used to things falling apart that I have no idea how to just enjoy it.  Does anyone know how to turn off this over-analyzing?  How do people reassure themselves that the bottom doesn't always fall out from under them?  How do I get the wheels to stop turning?  See what I mean about over-thinking!  I'm not sure the hamsters will ever get tired.  Suggestions welcome!