Final answer:
A patient suggesting alternative diagnoses or treatments when faced with an upsetting diagnosis is likely using the defense mechanism of denial, or potentially rationalization, to avoid emotional discomfort.
Step-by-step explanation:
When a patient is faced with an upsetting diagnosis and starts suggesting alternative diagnoses or treatments, the defense mechanism they are likely using is called denial. This is a psychological strategy where the individual refuses to accept reality or facts, thereby protecting themselves from the emotional discomfort associated with acknowledging what is true.
Another related defense mechanism could be rationalization, where the person might try to justify or explain away the distressing diagnosis with alternative ideas that seem more acceptable or less threatening.