Re: Is this overtraining?
Rest is fundamentally most important. If you are light headed, it is most likely that you are Anaemic. If you want to test whether you are Anaemic (Are you vegetarian by any chance?) you may want to take Iron supplements for 2 weeks and see what happens. Tablet form is best ingested with other food to make it more easy for the body to absorb. If you still feel light headed despite taking the supplements, go see a doctor.
Iron deficiency can also be due to biological factors. Your haemoglobin may not be carrying enough oxygen, and most haemoglobin tests can be done at any health check centre. An average person should have a haemoglobin level over 11 g/dl. Upper limit for most fit people at sea level is 16 g/dl.