I posted the same thing back in April. GPs have been told not to prescribe diazepam anymore (and if your GP is anything like mine, you can't get an appointment for acute, serious problems, so definitely wouldn't for fear of flying).
I was OK going actually. I read about lots of techniques, such as tapping, having upbeat music on headphones - it's the taking off I hate.
I did have a panic attack another time. Take off was fine, but I saw another plane, going the opposite direction, which alarmed me. It must have been 1000ft below, but it looked very close, I then became claustrophobic and wanted to get out.
I did take two codeine before this flight - thinking they'd subdued me, but I think that was the cause, so I wouldn't take anything like that again.
What I also found helpful was watching pilots on YouTube. When I had the panic attack, I also noticed the cabin crew keep going to the galley and pulling the curtains, I convinced myself there was an emergency. Now I know that's wrong, as that wouldn't happen in an emergency. I also know the different tones between calls from passengers and calls from the cockpit.
Although a lot of the pilots on YouTube talk about what went wrong during crashes, they also explain the different engine noises, how safe turbulence is and how well trained pilots are.
I totally get your fear, but honestly it'll be fine x