Chillaxed is the past form of chillax: you relaxed and became calm. Same young, informal feel — We chillaxed by the pool. People also use it like an adjective after a linking verb: He looked completely chillaxed. It does not name a new idea; it is only the “already done” shape of the same slang. Older or more formal English would just say relaxed.

放輕鬆了