When a person is having a seizure they'll usually froth or drool at the mouth, have muscle spasms, and even lose consciousness.
Sometimes the person will also start jerking while standing, sitting or lying down.
A person having a seizure can have visual disturbances or even black out completely.
Some people recover from small seizures without any medical treatment but if the seizure gets too severe then you need to call 911 and get medical help because when a seizure gets too severe it can be deadly.