Aidan has had non stop diarrhea all day and is severely weakened. why is his nurse concerned?

Diarrhea can be caused by indigestion, a raw meal, or little bacterias found in almost anything we swallow, but if it doesn't stop in a 12 hours period, it may be caused by some infection or a worse condition that need to be seen by a doctor, is this case, the nurse is concerned because Aidan is severely weakened, signal that is dehydrating very fast and that could cause him a worse condition such as hypotension, hypoglycemy or even losing consciouness.