Reactions after a frightening event are normal. Difficulty sleeping, replaying it, irritability, exhaustion, being startled by ordinary noises, not wanting to talk about it, wanting to talk about nothing else. These are what a nervous system does after a threat, not a sign that something is wrong with the person.
What helps, and is not complicated. Sleep, food and water at ordinary times. Routine, even a small one. Company. Something to do that has a visible result. Less news, at fixed times rather than continuously.
Children show it differently — clinginess, going backwards in things they could already do, stomach aches, playing the event out. Routine and honest, brief answers do more than reassurance does.
When to seek help. If it is not easing after several weeks, or it is stopping somebody working, sleeping or looking after themselves, that is the point to talk to a doctor. Say what happened; it is relevant.
And rebuild the supplies. Refill the water, replace what was used from the bag, recharge the power bank, check the torch. The period right after an incident is the one time everybody agrees it is worth doing — and the second event, when there is one, tends to arrive before the shops have restocked.