otherwise can either be an adverb of manner or a conjuction.
otherwise as an adverb of manner usually comes after the verb:
- I must be eaten slowly. Eaten otherwise (= in a different way) it is not as good as eaten slowly.
otherwise as a conjunction means "if not/or else":
- He must be ill; otherwise he would go to the party.
or could also be used here in more colloquial English:
- He must be ill or (else) we would go to the party.