There isn't much you can do to stop a seizure once it starts. But there are simple steps you can take to protect someone from harm during a seizure. It's worth knowing some basic first aid -- and when it's time to call 911.

Witnessing someone with epilepsy having a seizure can be truly frightening. But most seizures aren't an emergency. They stop on their own with no permanent ill effects.

Types of Seizures, Degrees of Danger

Some are more dangerous than others. There are two main types:

Focal onset seizures start in a single part of the brain. Her arm might start to move or her face start to twitch. And even though she's awake and aware, she can't control it. She might seem to zone out or stare at nothing as the seizure becomes complex. Afterward, she may not remember a thing.

Generalized seizures involve multiple areas of the brain at once. People are rarely aware of what's happening. The most well-known type falls in this group: the generalized tonic-clonic seizure, also known as a grand mal seizure. These are frightening to watch and can be an emergency.

They have a set sequence of events:

The person may become unresponsive. She doesn't answer if you call. She won't react if you wave a hand in her face or shake her. She may suddenly collapse.

Her muscles clench and she becomes rigid as a board. This is the tonic phase. It lasts a few seconds.

Next, a series of jerking movements convulse her body. This is the clonic phase. It can last a few seconds or several minutes.

Eventually, the jerking stops and she regains consciousness. She may be confused or disoriented for a short period.

Any generalized seizure can be dangerous because the person is unaware of her surroundings and can't protect herself from harm. The uncontrolled thrashing movements during a generalized tonic-clonic seizure increase the chances of injury. This type is most likely to result in a trip to the emergency room.