You characterized your "spells" as a fluttering of the heart with clammy skin, some shortness of breath, and subsequent fatigue. These "spells" could represent an intermittent heart arrhythmia. A relapsing and remitting arrhythmia can easily manifest itself with "fluttering of the heart" and the other symptoms you describe. Unfortunately, without knowing the additional details of your medical history, it is impossible to provide you with a clear answer as to what you are experiencing. Other considerations with an appropriate history could include anxiety attacks, vasovagal episodes, or even migraines.

What is clear from your description, however, is that these symptoms are burdensome to your life and have you concerned. Seeing your physician in timely order should be the first step to identifying their cause.