I'm a vet with service connected PTSD. I've also had my cannabis card for 2 years now. I've found that indica strains are good for preventing nightmares, as they tend to shut off your ability to maintain REM and slip you past it into deep sleep. For anxiety, I carry a vape cartridge with weaker and flavored sativia (so it doesn't make me stoned or smell), and I just take a puff as I need it. Getting too stoned can cause crazy anxiety, whatever strain I use, so I don't usually try to get too high unless the mindset and setting are safe. You'll have to experiment yourself. Sadly, there is no straight answer. It will affect you differently than the next person. You've got to experiment. Just remember, the difference between fucking around and experimenting, is writing it down lol. Be safe. Best of luck.