I heard a native English speaker said:
I am severely in need of it.
It sounds much better than
I am severe in need of it.
But thinking more deeply, isn't need a noun here hence it should be an adjective severe? Like "I'm good in shape."
But using adverb still sound more natural to me in many cases(but not the shape case above), for example "They inherently in genes are cute."
So what should it use actually?