Suggest Treatment For Nausea And Fever

For most of my adult life, I experience unexplained bouts of severe nausea. Sometimes once a year, sometimes I will go 2 or 3 yrs without an event. There are no other symptoms; no aches, pains, soreness, fever, etc. nothing. It comes on suddenly and without warning. I either end up in the ER,
or as just a few days ago, my doctor prescribed Zofran, which worked well. I am left feeling weak but am recovering well. But why would this happen to an otherwise healthy woman?