I always heard he went on an all day drinking spree with some friends.
from Wikipedia:
“No extant contemporary source explains how or why he died. Half a century later, John Ward, the vicar of Stratford, wrote in his notebook: “Shakespeare, Drayton and Ben Jonson had a merry meeting and, it seems, drank too hard, for Shakespeare died of a fever there contracted”,[66][67] not an impossible scenario, since Shakespeare knew Jonson and Drayton.”
Eh, okay. However, getting drunk doesn’t cause fever. Maybe he got dehydrated and then drank bad water.