Hi! These Past Few Days Ive Been Very Tired And

Hi! These past few days ive been very tired and I get dizzy very often, I also get light headed. Two days ago I sat up and all of a sudden got really cold and started shaking. My eyes felt like they were glued shut and my whole body felt very heavy. My boyfriend said that I was starting to warm up so he went and put cold rags on my forehead, he also said that when I finally looked at him my eyes were rolling to the back of my head. He tried to get me to stand up and when I did everything was black and I lost all balance. I went to work that next morning and didn't feel myself. I bent down at work and when I stood up my vision went blurry. About thirty min later about the same thing started happening like the night before. My manager said that my eyes were rolling again and I was spinning in my head and I was also shaking. After I have these spells or whatever they are I get very tired after. Today I was at church and we have to stand for 15 min and I felt like I was gonna fall over I was so weak. My eyes are very droopy as well. I have been eating quite a bit too so I know that its not from that. Today I have been very tired and I had a headache earlier and I have also been getting light headed and dizzy when I stand up. Do you know what could be possibly wrong? Do you think its serious?