What Could Cause Frequent Dizziness?

I was complaining again today of being dizzy when having to stand for more than a few minutes... I am almost always tired, yawn quite a lot and nod off during lectures. I am often cold and my hands, feet and nose are usually cold to freezing at the touch. I am pale at the moment.. but that probably has more to do with living in a cloudy place and staying indoors most of the time to study. I get dizzy often and have to sit down or I scan the room for a chair and obsess over it until I get to sit or at times even consider sitting on the floor. Sometimes my chest feels a little weird on the left hand side and I m sure my heart rate is faster than it should be. I also sometimes feel sleepy and somewhat nauseated after eating certain foods. My mother says I might be anaemic. I m not sure if it might be a thyroid problem or blood sugar levels (diabetes). although I know the symptoms for those and probably don t have half of them. I ve had a couple more serious dizzy spells where I felt cold sweat coming on, felt like the room and the people around me were distant, and had to squat down on my heels to almost sit on the floor until the feeling passed. It was a little scary and I had eaten properly for breakfast that day. The doctor I was shadowing (I am a medical student) asked me if I was hypoglycaemic to which I could only reply that I had no idea. It is very inconvenient to nod off during lectures and to not be able to stand for very long. What do you think I have.. what should I do to confirm it, a blood tests I presume?