I don't slap, but I ran into a lot of issues a few years ago resulting from three herniated discs in the cervical portion of my spine. Lost a lot of strength, developed tendinitis, couldn't play for about 6 months. That lead me to a different approach to playing music.
First, if you are injured - you have to let it heal. If you have a repetitive motion/strain injury, it will never get better if you continue doing the thing that caused it in the first place. I know that doesn't sound practical for a musician, but it's the truth.
Second, we aren't all created equal (physically). Some guys can play for hours every day for years and not break down. Others aren't so lucky. I would recommend you get a little stretching routine for the muscle and tendon group you're using for bass playing after you heal. My job puts me at a desk on a computer for most of the day. Between work and bass playing - it's a recipe for repetitive strain injuries. I stretch at work, and before I play bass. Sometimes if I'm just sitting in front of the tube at night with the wife I'll do some light stretching and motion just to keep the the arms/hands loose and feeling good.
Third - what seems like another no brainer, drink a lot of water. Ya' know that 8 glasses a day rule or whatever it is? If you aren't hydrated, all of those muscles and tendons are going to burn out quicker.