Good Morning,Gasping for breath is an anxiety symptom, its basis is usually an abnormal breathing pattern, usually hyperventilation. I expect you are breathing rapidly and quite shallow and more than likely using your upper chest. All of these faulty breathing habits cause the flight and fight response and the weakness that you describe.
Here is a link that explains hyperventilation syndrome: http://www.dynamicchiropractic.com/mpacms/dc/article.php?id=41073
It describes perfectly what you are feeling and I know from personal experience the discomfort and abject feelings that faulty breathing patterns can produce. There is a saying that the mind creates information you can act on but it is the breathing that makes sense of it all.
So the way out of it is this, take normal sized breaths using the diaphragm and slow your breathing rate to about 10 per minute. Practice for two minutes twice a day and increase slowly to 5 mins twice a day. Don't do any longer as if you are suffering from anxiety then extending breathing retraining can give you a panic attack.
As for your neck issues, see your Dr. as you may have an injury such as a sprain, pinched nerve etc.
Kindly,
Kitt