Drooling can occur for a number of reasons in cats. Probably the most commonly identified reasons are gum or teeth disorders. Oral ulcers can sometimes cause excessive salivation. Problems that lead to nausea, such as renal failure or gastrointestinal disease also cause excessive salivation. Some cats salivate excessively when they are nervous or stressed. This is a common reaction to oral medications and application of flea control products, too. Your vet can help sort through these possibilities and hopefully find a treatable cause.
Foaming at the mouth or excessive salivation is common when cats have ingested something more noxious than they expected it to be, when they are nervous, when they have been sprayed with a spray containing alcohol (many flea sprays are alcohol based), when they are nauseous and with a few diseases such as dental disease and calicivirus. There are probably other causes. A brief episode is probably related to ingesting something that was upsetting. I have seen this after one of my cats ate a spider. Licking toads will do this, too.
Hair balls are obviously one cause of feeling nauseous. If you live in an area with heartworms it is another cause of the hacking and vomiting problem some cats have. Inflammatory bowel disease is another. Your vet can help sort through these, too. In general it is a good idea to consider pursuing a diagnosis of vomiting if it is occurring frequently and coughing is almost always abnormal