Would suggest making a time boxed plan which you can control such as
1. Bring things to do/watch/listen to to keep distracted and power bank + spare cables. Charge everything before going to the airport.
2. Find a "virtually soothing space". If I can't sleep, I tend to listen to some specific white noise tracks or music which helps me relax and which I've heard before. Then I close my eyes and if I doze off or it gets to that weird in-between sleep state, no big deal. If I stay awake then that's fine, too, especially if I have time to get a bit of rest afterwards. Even "resting your eyes" should help your body get a bit of rejuvenation. Since you have sleep disorders, I'm sure you've had some nights where you could not rest very well but still made it through the next day. Sure, it'd be nice to sleep on a flight but it's kind of a stretch goal for most on a 16 hour flight in economy. Plenty of other people will also be awake, even without flying anxiety, because a plane isn't the easiest place to sleep and 16 hours is a long time for some people to stay seated. I also like noise cancelling headphones to help cancel out some engine noise. Maybe your sounds are ASMR, old sitcom you've watched a lot and fallen asleep to, lulling audiobook.
3. Make your "comfort in flight" packing list, even go ahead and pack it several days before. If small food bribes make you happy, pack your favorite snacks. Bring layers of clothing, snacks, wipes, sanitizer, masks, etc. I pack oxygen activating heat packs and a travel blanket because I can't sleep when I am cold and get cold easily.
4. Read the safety card thoroughly and locate the exits after boarding.

So now you have a plan which works with your own coping mechanisms. Perhaps you've worked on it with the therapist. Now try to stop dwelling and freaking yourself out. Try to stay busy offline and away from YouTube/Netflix flight related content. Unless you work with negativity and fatalism, watching such things with negative flight incidents is not going to help your stress levels.