When hiking and camping I never seem to have any problem sleeping. The fresh air, steady exertion of carrying a pack and covering ground, stars above, and a stress-free environment away from people and work see me out like a light and up with the sun.
A wilderness survival situation may share enough of that so sleeping may not be an issue. The situation after a major disaster where hundreds, maybe thousands, are homeless, injured and in desperate need of the basics shares few of the things that makes sleep easy.
Odds are you have lost most of what you had: friends, family, home, even all those carefully socked away survival supplies may be gone. The future may be doubtful because the place you worked, the people you worked for and with may be gone. What worries you the most is simply not knowing. Not knowing who made it, who didn't. Not knowing how you will cover the basics tomorrow. Not knowing how you will make a living.
And then there are the other people. People who have been ripped out of comfortable lives, some of who are injured, all sharing the same doubts and fears. Uncertain, frightened, with no clear answers.
If you are around people they will be testy, angry, nervous, in deep denial, catatonic, or suicidal. Many doing each by turns. The injured will cry out and moan, kids will whine and scream and cry, adults will bicker over nothing. The best and worse all come out. Near crowds there will be constant noise, commotion, smells. Sleeping is going to be an issue.
Earplugs, a sleep mask, a smear of Vapo-rub under the nose help a lot. Benedryl has its uses. Some people like a pink-noise recording on a pod. Never had one of those. I've used my sleep kit on a buses and in airports. Being a little isolated by these I usually alert a few people to bump me awake if anything happens.