Could it be hypoglycemia or low blood sugar? When do these episodes come on? With hypoglycemia you can feel the following symptoms:
nausea
weakness
shakiness
paleness
Hypoglycemia occurs when the blood sugar concentrations fall below a level necessary to properly support the body's need for energy and stability throughout its cells.
For me, my hypoglycemia was so severe I'd pass out. I had this for years, since I was a teenager, and finally got diagnosed with hypothyroidism over 30 years later. The hypothyroidism was the cause of my low blood sugar.
Before I got diagnosed, I had to eat every two to three hours or feel as if I would pass out. The symptoms worsened when my hypothyroidism worsened.
Does it happen when you are stressed or anxious, sounds like it could be anxiety, i suffered from it for years. Your gp could refer you to mental health for an assesment
it sounds like a panic attack... u should speak to a neurologist in order to rule out something neurological and then go se a psychiatrist... i wouldn't worry, the most likely cause is a panic attack :)