Before the appointment
Write three things down: (1) what you are experiencing in plain language, (2) how long and how much it affects daily life, (3) what you want from the visit (referral, time off work, medication discussion, blood tests).
During the appointment
Lead with the strongest sentence first ("I have been thinking about ending my life" / "I have not slept properly in three weeks"). Ask explicitly: what are my options here, and what is the next step? Take notes.
Follow-up
Book the follow-up before you leave. If you feel unheard, you are entitled to a second opinion or to see a different GP at the same practice.