I’ve had good luck with avena sativa as a sleep aid, but occasionally take it during the day to take the edge off. But too much and you get drowsy. I use the 20:1 extract powder:
One-quarter teaspoon would be a good trial dose to see if it has any effect. I’ve researched it a good bit, and found nothing about it being habituating or developing tolerance, or any drug interactions. Pretty inexpensive. Might be worth a try.
The other things that help in general are regular vigorous exercise and a regular mindful meditation practice. With meditation you learn to focus on the here and now, rather than worrying about bad things that happened in the past, which you can’t change, or that may happen in the future, but probably won’t. For something like a panic attack, it might help you to mentally step back and become an observer of the attack, and thereby reduce your emotional involvement in it.
But Google avena sativa and anxiety, and see what comes up.
Avena sativa is just the Latin name for oats.