It is tired respiratory muscles.
I am Dr. Prakash HM and I will be answering your query.Cough
is reflex action.
During cough, the muscles of back, shoulders and chest are all involved.
As you were coughing for quite some time, the muscles would have got tired due to accumulation of lactic acid (due to continuous extra work).
Any extra action involves, overworking the muscle and this you are feeling like pins and needles.
As you are trying to remove, more phlegm using the medication, deep action is involved and you are feeling like it.
Normally, it would be severe pain
and and in the elderly, do to altered neural sensation, you are feeling like pins and needles.
Once you limit your coughing, the pain will reduce.
Cough suppressants can be used, but not now, when you have active phlegm production.
Any further queries, happy to help again.
Dr. Prakash HM