This sounds like something neurological. You may have a blockage or growth somewhere that's affecting your nervous system. This can develop into a very serious condition. It could also be heart related. However, the muscle weakness
and rigidity you describe definitely sounds neurological. The only way to tell is to go see a doctor right away, and I'm glad you're taking that step. I don't see this as something that will go away on its own without treatment. Good luck.