Alicia: I think her worst fear is something terrible happening to the people she loves. Definitely way more than she fears harm to herself, she fears them having to live in misery or suffering. But she also fears loneliness, and not being loved. Her worst dreams are a tie between the ones where she relives the accident, and the ones where she and Kattar are a couple, but then she has to wake up.
Kattar: There's a LOT to unpack here. His worst fear is being useless, and living up to his mom's opinion of men. His worst fear is that he'll fall out of favor with his mother, and be left without any parent at all, because he's never met his dad. His worst fear is that the paralysis will get worse and he'll be completely and entirely helpless until he dies...and more. Without giving too many spoilers, he has a lot of fears, but most of them, he's always kept bottled inside, and he's just starting to be honest about them now, at the 38th chapter, so it's going to continue forward from there.
His worst nightmares are probably reliving the day she started dating Etan.