 This small study is designed to provide information on whether MDMA-assisted psychotherapy is safe and helpful for people with anxiety related to a life-threatening cancer or neurological illness. The research is to see if psychotherapy combined with MDMA in a therapeutic setting can ease anxiety in the face of a life threatening illness. Once enrolled in the study, people will either receive two day-long psychotherapy sessions with MDMA or placebo, with five people getting placebo and 13 getting MDMA. Anxiety, depression, sleep quality, attitudes toward death, posttraumatic growth, mindfulness, self-compassion, and overall quality of life will be measured at the start of the study and after these two sessions. People close to the participant will also complete questionnaires about the participant during the study on their mood and behavior. Participants who received placebo can enroll in Stage 2, during which they will receive three psychotherapy sessions with MDMA, and participants who received MDMA will have a third MDMA-assisted experimental session. Anxiety and other symptoms will be measured again six and 12 months after each participants final experimental session. 