Yes during severe dehydration memory loss is a symptom of severe memory loss in people.
Other symptoms of memory loss besides dehydration are confusion, drowsiness, dry mouth, increase in thirst, dizziness, headache, dry skin, low volume of urine or urine that is more yellow in color than normal.
Severe dehydration needs medical attention because it can be deadly so if you think you or someone is severely dehydrated you need to get to the hospital for treatment.
You should also aim to drink 8 glasses of water or other hydrating fluids throughout the day even before you feel thirsty.
Drink something to stay hydrated long before you begin to feel thirsty to keep hydrated properly.