Hi, I'm sorry to hear that you're having this, I'm sure it's frightening.
When they diagnosed you with SFN did they do a "sweat test?" it's sometimes called a sudomotor or Qsweat test. That test is for autonomic neuropathy which affects your autonomic nervous system. You can do a google search of everything the autonomic nervous system does but I do know that it controls you blood pressure and sometimes those episodes of lightheadedness can be related to that. I also have autonomic neuropathy and that was something my neurologist asked me to keep an eye on. Good luck, I hope you find the cause.