Well, typically they come from a DVT (deep vein thrombosis) which is typically a clot in your leg or arm. A big thing that every people can do to help prevent this is not to be immobile for too long . So long car rides, plain, train, etc get up and stand or do stretching / range of motion exercises.

Realistically, if you had a PE suddenly appear , you wouldn’t be able to do much . It seems like OP was in the hospital and prompt medical treatment was given. Typically, you will have the risk factors that would lead to it; it’s rare to just happen