Anxiety attack, panic attack, asthma attack, a bad enough upper respiratory infection, and probably a myriad of other things.
Try sitting (or standing) straight with your hands on top of your head to help expand your rib cage. Do not slouch. You want your lungs to be able to expand as much as possible. Try slow, deep breaths (as much as is comfortable without causing coughing). Focus on getting calm.
You can try boiling some water or using a vaporizer. Sometimes this can help with a mild asthma attack, especially in combination with an emergency inhaler. Do note that an asthma attack not helped by an emergency inhaler may need medical intervention (i.e., nebulizer provided in the ER). Fresh air can help as well, though if you're in northern Cali, that may be impossible right now.
Do note, if you are taking an emergency inhaler, it is recommended to expel all air, inhale one puff, hold a few seconds then release. Wait about 5 minutes for the next puff to allow for the first one to begin working. Taking it immediately after the first will not allow the treatment to be as effective.
Get somewhere quiet where you feel safe to try these things. If it's an anxiety attack or panic attack, this may help. Do not be alone in case this is more than an anxiety or panic attack.
Do note that breathing issues can be considered a medical emergency, if they are not helped within a reasonable amount of time by normal at home intervention. Please go to your nearest ER if this persists and does not get better in an hour or two or suddenly becomes worse.