welcome iris

there are many things that can trigger an altered state

it is important to identify the trigger event, so your doctors can pinpoint the possible causes

eg
past event PTSD

LSD psychosis flash backs

light patterns epilepsy

food allergy epeilepsy

sleep deprivation altered state

psychological trigger

its interesting you mention thirst, has your BF been checked for diabetes, is hydration a factor

thirst is governed by the automatic nervous system centered in the brain stem there is a condition known as POTS that can cause this system to be effected

because this happens so infrequently its important to find the trigger so the doctors can image the event

try to push for an earlier appointment

it may be none of the above

best wishes

http://home.att.net/~potsweb/POTS.html