maybe you could be anemic you said weak at the knees and lightheaded im animec an i get weak tierd lightheaded neausa ect so try asking your doctor to check your blood to see if you are anemic alot of pplz have died not knowing that they have been anemic
My mother had that problem and it turned out to be bulging discs in her neck that were constricting some nerves. There could be lots of causes of lightheadedness, so you might want to see a doctor to get checked out.
Low blood sugar ask the doc to check your sugar levels ..doesnt mean you are diabetic, when you feel light headed try ea ing some carbs even a glass of juice ,if you feel better its hypoglycemia