When this first happened to me ten years ago, I was really disappointed with a couple of friends who behaved like I had a contagious disease. This time round I have a better handle on what I can expect from the people around me.
It's infuriating to hear about how their lack of attention was all about how you made them feel.
They will tell you that they didn't know what to say, that they didn't want to bother you, that they couldn't stand to see you sick, that they had the flue/HIV/hepatitis. They have to leave the country, lost their phone for 6 months, lost your number, have sick parents in Iceland, were having an affair/trouble at work/renovating their house. Phhffft.
While all that is going on, people you may have underestimated or not known well will step up and surprise you. If someone who is just an acquaintance offers help, take it.
Critical illness does polarise people, it's not something you can do much about, apart from cultivating the people who are on your side.