If you need a catheter, what's the alternative? The reason you sometimes get one is because your bladder is the last thing to wake up from the spinal, and you can't "go" until it does. If you gotta go, you gotta go!!
I guess you could take your chances and wait and see if your bladder wakes up before you need to go. That was the approach in my hospital, where I was told they didn't fit one automatically, but wait until you decide if you need one.
It's nowhere near as bad as your imagination is probably telling you, and neither is the spinal. Try to relax.