Excessive perspiration

I am a 34 year old healthy female.  I have been having episodes that I can only explain as 'hot flashes' I will sweat profusely from waist up to forehead with sweat beads and it goes through my shirt in the under arm area, stomach and back.  I've been to an endocrinologist and we did blood work, they came back fine.  Now she wants to do another round of blood work and a saliva test, but I was told it is extremely rare since the first round came back fine.

I asked what do I do if these tests come back fine and was told I would need to see a neurologist/auto immune specialist.

Any ideas what is causing this?  it is very distressing and has no warning signs or no 'attack' has anything similar.  It occurs when I am outside, inside, little or no activity.  It is starting to affect the quality of life as I do not ever want to leave because it is so embarrassing.  Any help? advice? guidance would be extremely appreciated.