Couple of things to try...
(1) Meditation: Put on some chill music or a meditation/hypnosis script, get into a comfy bed or couch, dim the lighting and use lava lamps if you have any or mood lighting, and just relax. This will work the best in most cases.
(1.5) Massage: In addition to the first point, if you have someone nearby, get a massage done.
(2) Masturbation or Sex: This really works to eliminate problems. Depends how much stims you took though, but an orgasm as the best anxiety reliever there is.
(3) Exercise: Doing lots of cardiovascular exercise in fresh air and sunlight is like a combination of factors which can seriously demolish anxiety and panic attacks. Although it may be hard to exercise while panicking, after you do it, you'll feel much more relaxed. Strength training does wonders if you do it frequently, but even hitting the weights or punching a bag is an extremely useful and underrated method that quells this problem. Plus having a nice body helps with social anxiety.
(4) Nutrition: Basically a lot of anxiety is actually a deficiency in some nutrients. Magnesium, B vitamins, omegas, zinc, and a bunch of other stuff can do a lot to reduce it. Strangely, I've found that sugary carbohydrates work for mental anxiety, whereas protein/fat helps with physical anxiety. Cereal and steak are my favorite food choices, along with smoothies, for this stuff.
(5) Other Drugs: Benzos are the #1 choice for counter-acting this in stims. Kava kava, valerian root, and St. John's wort also pretty good overall. Melatonin really helps to take after a stim binge.