Clinical pearl: the phrase impending sense of doom plus choking and palpitations, with a normal physical workup, is the textbook description of a panic attack.
Eliminate the rest. Asthma is removed first because the respiratory examination is normal, with no wheeze or distress on auscultation. Epilepsy does not fit, as there is no seizure activity, aura, or post-ictal state, just acute anxiety. Depression is a sustained disorder of mood and anhedonia over weeks, the opposite of a brief explosive episode of fear.
The remaining answer, panic disorder, captures the recurrent, abrupt episodes of overwhelming anxiety with prominent autonomic symptoms (chest tightness, breathlessness, palpitations) and the dread of doom, all in someone whose organic evaluation is unremarkable.
Ref: Arvind Arora Review of Psychiatry.