The phrase "off head" is typically used to describe someone who is acting erratically or irrationally. There are several synonyms for this term, including "crazy," "unhinged," "out of control," "wild," and "mad." Other phrases that convey a similar meaning include "losing it," "freaking out," "going bonkers," and "losing one's mind." It's important to note that these terms should be used with caution, and should never be used to stigmatize or shame individuals who may be struggling with mental health issues. Instead, it's best to approach these situations with understanding, compassion, and a willingness to help those who may be struggling.