I've observed that my ocd obsessions can recombine with each other, and persist over many years. At age 8 or 9, I became hypersensitive to any sensation of pressure in my bladder. I'd get up multiple times to make sure there was not a drop left in me, because I had the obsessive thought that I wouldn't be able to fall asleep if I didn't. When I went away to college, I had a room mate who was swigging cranberry juice in hopes of warding off a bladder infection. I'd never heard of bladder infections, and my ocd was immediately hooked. My fear of a full bladder melded with fear of getting a bladder infection.
On my 21st birthday, I had a sudden heavy ache in my pelvis. Stress makes my ocd worse, as does having a lot of free time, and this was a very lonely and stressful summer. I went to an urgent care center and the doctor treated me empirically for a bladder infection, ie. he figured that's what it was, and didn't do a urine test.
Right before my 27th birthday, my symptoms returned and I agonized about seeing a doctor, afraid I was weak, and wrong in my self-diagnosis. The nurse did a rapid test and said I had an infection. I felt a bit of relief, but then I got a headache, and feared it was from the antibiotic. I descended into health anxiety hell, into constant monitoring of how I felt, into fear of every sensation, every unknown, a dogged headache, and feeling dazed and overwhelmed when in the sun. I called the drug company hotline and they told me it wasn't the medication. I finally went back to the doctor, who diagnosed flu and gave me darvocet to help with the headache, but which only exacerbated my obsession about medication side effects. My infection symptoms went away, but my obsession with a bladder infection remained, and my fear of it spreading to my kidneys, of being condemned as negligent for not coming into the doctor sooner, and fear that I could bring on an infection by thinking about it.
On my 34th birthday, on vacation, I started worrying I had an infection. I went to the bathroom at a restaurant, and I felt a sensation of warmth, and panicked. I drank cranberry and water, with constant monitoring of my how my bladder felt which of course felt full. Later, I could look back and note that in a chilly air conditioned restaurant, chances are that the fluid in my bladder is going to feel warm. In the night, after getting up to drink water every 1/2 hr, I sat down with my journal and wrote about whether I really believed that I could cause an infection by thinking about it. I took a leap of faith and stopped drinking the water that night, and went back to bed. I was scared as I laid down, scared of the dizzy feeling of being on a precipice of anxiety, but I knew unless I took the risk of resting, rather than compulsively drinking fluid, I would be a captive.
OCD compulsions have an uncanny way of creating the very condition that you fear. Constantly checking my bladder made me hyperaware of every bit of pressure. Drinking constant fluids, in hopes of diluting any bacteria, created constant urgency to urinate. Trying to get rid of thoughts of getting a bladder infection made me focus on it even more.