we can consider the following possibilities as you havenot given many clues. 1) pheochromocytoma 2) paroxysmal dysrhhythmias 4) thyrotoxicosis 5) anxiety with panic attacks 6) Postural orthostatic tachycardia syndrome (POTS) Usually pheochromocytoma is associated with paroxysms of elevated blood pressure , sweating and palpitation. A 24 hour urine metanephrine and normetanephrine will practically diagnose this condition. Any transient Supraventricular or venrtricular arrhythmias can cause the above symptoms for which a holter monitoring will help. But last and perhaps the most important consideration will be anxiety with panic attacks especially if you have baseline stress or fear (phobia). A consultation with a psychiatrist / clinical psychologist, analyzing the stress factors if any and avoiding the situation which precipitates the same will address the present situation. try anxiolytics (eg clonazepam ) and if useful you can continue the same under supervision. A Thyroid function test to rule out thyrotoxicosis and a blood pressure and heart rate monitoring while standing will help the diagnosis of POTS Hope my answer didnot confuse you further/ definitely we can aid you throughout