How dangerous is apnea? My husband wakes up suddenly and runs from bed. What causes this? I am worried he might do sth and not even know abt it.

Can be dangerous. Apnea can be dangerous, even deadly if not identified and treated. If you suspect apnea, see your primary provider to be referred for a sleep study to confirm. Treatment options can be discussed if the sleep study is positive.
Apnea is serious. Sleep apnea is associated with lots of other diseases: high blood pressure, heart problems, bad heart rhythms, daytime fatigue, weight gain. There are also serious medical problems that can mimic sleep apnea. I'd trust your gut feeling about sleep apnea and encourage your husband to see his doctor. Good luck!
MAY NOT BE APNEA. If he snores loudly and frequently stop breathing for 10-15 seconds, then takes a loud gasping breath, this is probably sleep apnea. If he jumps out of bed and has trouble breathing for seconds to minutes, the problem is probably reflux causing vocal cord spasms. An ENT doctor can easily settle the issue. Apnea is dangerous and can cause heart attacks and strokes.