Bad is often used as an adverb in sentences such as The house was shaken up pretty bad or We need water bad. This usage is common in informal speech but is widely regarded as unacceptable in formal writing. In an earlier survey, 92 percent of the Usage Panel rejected the sentence His tooth ached so bad he could not sleep

want badly

The use of badly with want was once considered incorrect but is now entirely acceptable. So don’t feel bad if you find yourself wanting to go to the beach badly

feel badly

If you say I feel bad, people may think you have a cold, or they may just as likely think your spirits need a lift. But what if you say I feel badly? Will you get sympathy, censure, or an aspirin? The adverb badly is often used after verbs such as feel, as in I felt badly about the whole affair. In fact, this usage bears analogy to the use of other adverbs with feel, such as strongly in We feel strongly about this issue. Many people like to restrict feel badly to refer to emotional distress and let feel bad cover physical ailments. There is nothing wrong with maintaining this distinction, but don’t expect everyone else to share this view. It’s another useful distinction that is often ignored. Be sure that readers will understand feel badly from its context.

badly meaning “unwell”

In some regions people use badly to mean “unwell,” as in He was looking badly after the accident. Poorly is also used in this way. You may want to be careful with this usage, however. In an earlier survey, 75 percent of the Usage Panel found it unacceptable in formal writing.