It feels like I got this 800 pound gorilla on my chest

A therapist was working with a person on stress management, and this is how the client described his stress. This is a mashup of “the 800 pound gorilla” (a person or group so powerful that it does not need to heed the rules or threats by others) and “get (something) off (one’s) chest” (to unburden oneself). While neither idiom relates to the subject matter (a double incongruent conflation?), it appears the speaker was conflating the two phrases. A big thanks to patrickwardphd for hearing this one and sending it in!