Put them under duress by pressuring them to do something they do not want to do. This will almost certainly increase their anxiety. Pretend you are unable to help even though they believe you are unable to assist them at this moment, you may be able to assist them at a later time. Furthermore, simply knowing you are there to assist them is a tremendous help. You should never advise someone to breathe into a grocery bag during a panic attack. This isn't advised, and it could be dangerous.