If Daniel has nyctophobia,,,

[Alardem]

perhaps his experience during this expedition was the cause of him getting it in the first place?

The shadow coming after him may have increased it too, maybe the shadow generated the phobia.

I kind of wish the Shadow was literally just the evil darkness - it'd explain why you counter-intuitively fear the dark (which protects you from monsters) rather than embrace it, and I find it much more creepy than some goofy fleshy thing that roars.