system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do you go from feeling completely normal to having to violently and uncontrollably sneeze 5 times in a row out of nowhere?
gpt
The cause can be mild dehydration and subsequent recovery.

When you are dehydrated, your body starts rationing water.  High priority uses, like maintaining blood pressure and clearing dust from the lungs still get their share.  Low priority uses, such as draining the sinuses, get less than their usual share.

When the body is rationing water, dust that gets in the sinuses gets trapped by mucus, and sits there, but does not drain.

This is a perfectly normal way for the body to operate.  It is a natural response to evolving in conditions of intermittent drought.  It probably occurs daily for most of us.  ( This is why drinking lots of water is recommended when you have a cold.  It prevents the occasional local dehydration that would give the bugs a chance to get another foothold. )

When your body gets more water, then the low priority users get more.  ( BTW, this doesn't necessarily require drinking.  Sometimes your large intestine starts squeezing the water out of a bolus of digested food.  You get more water and you aren't even aware of it. )

When a low priority user like the sinuses regains its normal supply of water, they attempt to regain their normal functioning.  In the case of the sinuses, this means vigorous sneezing to get rid of accumulated dust.