Hi K Jones,
Welcome to HCM Forum,
I can understand how much disturbed u might be feeling.
From description given by you there can be possibility of two kind of illness u might have
1) Panic disorder ( where attacks are spontaneous,unprovoked, lasts for few seconds to minutes -characterized by chest tightness
,coldness-sweating of extremities,dryness of mouth,heaviness of head and impending doom)
(where sudden onset for fraction of seconds loss of consciousness
,sometimes associated with limb movement,confused behavior later on )
Both illness can look similar but can be differentiated by experts and with help of investigation like EEG,MRI brain etc.
Remember that both illness can be treatable.
So please consult to your nearest psychiatrist
,who will asses and start treatment accordingly.
Hope it helps.Best Regars.