severely vs gravely

severely and gravely both are adverbs.

Word	Noun	Adjective	Verb	Adverb
severely	No	No	No	Yes
gravely	No	No	No	Yes

As adverbs, severely and gravely are synonyms defined as:

Other synonyms of severely include badly, seriously.

severely (adverb)	gravely (adverb)
to a severe or serious degree	in a grave and sober manner
with sternness; in a severe manner	to a severe or serious degree
causing great damage or hardship