Does a muscle relaxer help with anxiety?

Technically no: A muscle relaxant technically affects skeletal muscle function by decreasing muscle tone. Muscle relaxants generally lead to sedation which may ameliorate anxiety. You may be thinking about valium which has been used in the past to treat anxiety. However, the level of sedation makes valium a poor choice today. Generally, physicians would prefer behavioral approaches for treating anxiety.

Exposure therapy: Find a therapist specializing in treating panic disorder. Especially helpful is exposure based therapy, where gradually, w/ the therapist's guidance, you repeatedly face the feared situations & symptoms of panic, along w/ relaxation techniques. Doing this over time, the physical sensations that accompany the panic feeling will no longer trigger a panic attack. Muscle relaxers not a good solution.