If you know someone who's had a seizure before, it's good to know how to help if they have another one.

So, let's take a look at what you can do, and if there may be times when you need to call 911.

The most important thing is to stay calm.

That may not be easy, especially if you see someone shake violently or pass out.

But staying calm will help you keep the person safe.

So here's what you need to do.

First, try to guide the person gently to the floor if you can.

Move any furniture or objects out of the way so if the person moves around, they won't get hurt.

Gently roll the person onto their side so that any fluid can leak out of their mouth.

Don't try to hold them down or keep them from moving, and don't try to put anything into their mouth.

If you can, keep track of how long the seizure lasts.

Because if the seizure lasts longer than 3 minutes, you'll need to call 911.

But usually a seizure lasts about a minute to a minute and a half.

When the seizure is over, check the person for injuries.

Loosen any tight clothing, and let them rest.

And stay with them until they're awake and seem to know where they are.

Now, here are a few situations when you need to get emergency help.

If the person stops breathing for more than 30 seconds, call 911 right away, then start rescue breathing if you know how.

Call 911 right away if the person having the seizure is pregnant, has diabetes, or has had a head injury.

And call 911 if this is the first time the person has had a seizure, or if you've seen this person have seizures before, but this time they aren't getting back to normal as expected.