If you sneeze or throw up a lot, can that sometimes lead to a retinal detachment?

Unlikely: Very unlikely. But possible. More likely, the retinal detachment would have iccurred anyway.

Unlikely: If there were a pre-existing condition such as a posterior vitreous detachment, high myopia with vitreous traction, etc. One could make a case that the sudden head movement could cause the vitreous to suddenly cause a retinal tear and detachment but that would be very unusual. The big question is why your are sneezing and throwing up a lot? You need to find out.