hello.i think you should take this seriously since you say you had a minor heart attack in the past.although stress test is normal it cannot show the functioning or the contractility of heart. there are more chances of previous cardiovascular disease giving rise to cerebrovascular disease, in your case it could be a TIA (transient ischemic attack) if you have completely recovered from it. if you had a shuddering feeling it could also be a seizure episode of any etiology which needs to be investigated.that numbness could be post seizure(todds palsy). you did not mention whether anybody in your family witnessed your episode(to know the level of your consciousness during episode) and also if you are on any medications like antiplatelets which are helpful in preventing such episodes. so please get yourself examined and investigated by a physician as early as possible. all the best.