"I have a fear of lightning" should also be acceptable
It should be the default IMO. Is "lightnings" still used by anyone?
you don't pluralise lightning... not sure you ever did
"Lightnings" is very old-fashioned, but was in fact used in the past.
It occurs 14 times in the King James Bible of 1611.
So, never come to Brazil!
Thanks for clarification. You are always very informative.