Your symptoms are typical of hypoglycemia, as suggested by margypops.
You require either a fasting and glucose tolerancfe test or what is called an insulin clamp protocol.
In the fast test you are instructed not to eat for a certain number of hours, your blood glucose level is measured, you drink a specific amount of glucose, and then, for a number of hours at specific intervals your glucose levels are measured.
You should be a "little nervous" and making an appointment for such an evaluation should be a priority. The blood sugar levels does not fall because "you have not been eating properly". It falls because the body's homeostatic mechanism has failed and the cells in the Islets of Langerhans are not functioning properly. This is a hardware, not a software problem.
Could be low blood sugar ( Hypoglecemia )have you eaten a while before you exercise, not immediatly before but a hour or two, it is possible that it has fallen if you are not eating properly. With these symptoms always best to go for a check up.