The _why_ of the sleep problems is separate from the _fact_ of it.
Whether the _why_ is suitable to mention is totally context-dependent. In some situations it would make sense to mention the why. In others it would be weird and going into too much detail.
And it’s not just nerve discomfort. It’s muscular and there’s all sorts of details that are not easy to describe if I want to actually explain what it is.
Finally, you’re assuming that mentioning the reasons would somehow mean people wouldn’t then make assumptions, and this is false. If I mentioned the why they’re likely to assume (I know this from experience) irrelevant causes/cures to do with pain (much of the problem is very different to pain), pillows, mattresses, yoga, etc.
I have also found that it does not matter what you tell people the causes are, many will not let go of the idea that the sleep problems must actually be the result of psychological causes, due to being unable to relax, a restless mind, poor sleep hygiene, etc.
It's actually not. It's 100% your team's business that you're underperforming, period, but any reason you give is on your dime. Since you're giving reasons, it is in your personal best interest to communicate to your team a need for reasonable accommodations under the Americans with Disabilities Act even if you don't describe to them the details of your condition.
I assume that people won't tell you to drink less coffee if you say something specific to your circumstance like "nerve discomfort keeps me awake at night" rather than something vague like "I have trouble sleeping".