What Causes Hypoglycemia?

ok ive been having the symptoms of hypoglycemia going on 4 days now, when i eat something i feel better but only about 30 minutes. nothings changed in my diet for years. same routine, work out a little every other day. nothing new, but my dizzyness and confusion, concentration levels, and eye sight are affecting me, i get up from bed in the morning with a headache, and all the symptoms above, and when i eat or drink something im fine but the symptoms come back almost emediate unless i eat i full course meal. then it takes about an hour. nothing like this has ever happened and im usually making sure im in good shape, im just wondering if somethings wrong i may not know about, and if you can help me i appreciate it every much.