If you are looking for earplugs that stay in whilst sleeping then you need a pair of moulded sleeping ear plugs. Many people who use the foam variety find that they fall out during the night. There are two reasons for this. The first is that the ear canal tapers and the foam expands whilst they are in the ears. This means that they push themselves out. They fall out during the night and you wake up.
The second reason is that earplugs come out during the night is due to irritation. Foam ear plugs expand, pressing on the delicate skin that lines the ear canal. Sometimes this is the reason people take them out in the night, often thinking they have fallen out.
Moulded plugs are much more comfortable and because they are formed to your ear canal they fit like a hand in a glove and so stay in during the night. Because they do not expand in your ear they do not press on the delicate skin or work themselves out.
ZenPlugs are far better than other types as you can make them yourself at home in a few minutes. This means they cost much less then visiting the audiology clinic. They are also antibacterial and so help to prevent ear infections from wearing ear plugs frequently.
Summary. If your earplugs fall out during the night get yourself a pair of moulded earplugs. They are far more comfortable and stay in.