From Wikipedia’s page,
It is often caused by a blood vessel pressing against the seventh cranial nerve (CN-VII). When blood flows it excites the nerve and causes the spasm.
If you or someone you know has this, look for a surgical solution called MVD, Microvascular Decompression (Wikipedia article). MVD consists of placing a teflon felt “spongy” material between the offending blood vessel and CN-VII to act as a shock absorber and spacer between the two. There are other treatments for the symptoms, such as medications, and Botox injections every 12 weeks to deaden some facial muscles, but the MVD treats the cause.
I suffered from HFS for 8 years. I tried many meds unsuccessfully, and did Botox injections for 5 years. I also tried acupuncture and acupressure. I finally went for the MVD surgery last June and it worked - I am now 100% spasm free!
I am now a big fan of the MVD solution. Hindsight being 20-20, I wish I’d done it sooner. As always, YMMV, and please do your own research, and consult neurologists.