If a trigger; such as cats sets off an asthma attack, try the following exercise: -
Lie with your back on the floor, holding your arms above your head and stretch your arms out and point your toes. Feel your shoulder blades on the floor.
Breath in for two and out for two. Take your breath from the bottom of your stomach and not the top of your chest.
Try to clear your mind and visualise fresh air; a mountain scene, snow topped mountains, clouds.
Continue until you feel more in control and the panic subsides. This will take as long as it takes.
Hope this helps. Helen.xx