Of course, hostelling involves a lot of sharing. I was not thinking of hostels though. I am a life time member of Youth Hostels (now called HI).
I have stayed in a shared room in a hostel, as well as a private room. I have even used a hostel with my family if they had a family room or we could get the whole room. Some hostels are quite nice, no less than a nice Guesthaus. There was one in Austria with two levels, like an art studio.
When you stay in a hostel, people you share a room with are already registered as guests with the hostel. In a way, they are indirectly "known" to you or introduced to you by the hostel, so to speak.
I don't know how hostelling would work for me with my CPAP.