I get light headed all the time but it's nothing to do with iron levels (I eat a lot of red meat and vegetables and had it checked when I tried giving blood) so for me I think it's more to do with how much I actually eat; when I'm at work I work strange hours and end up missing dinner so don't have anything to eat from 12 until 9/10pm which isn't great if you're on your feet for hours without a break.
If it's persistent, speak to a doctor who can clarify whether or not its an iron deficiency or something else. Don't be fainting on people!
It is very likely that because you don't eat much in the mornings and just carrying on throughout the day, you are using up your energy too soon. The feeling you get is called Hypoglycemia. (Low blood sugar), this happens because theres an inadequate supply of glucose to the brain, resulting in impairment of function (neuroglycopenia). The getting up quickly is called the vasovagal episode or vasovagal response or vasovagal attack. Vasovagal syncope occurs in response to a trigger, with a corresponding malfunction in the parts of the nervous system that regulate heart rate and blood pressure. When heart rate slows, blood pressure drops, and the resulting lack of blood to the brain causes fainting
I also get it occasionally, usually because I work in the Art studio. Throughout the day I'm exposed to all sorts of chemicals and I've noticed if I don't eat anything and work in there for a few hours, I will feel really light headed, dizzy and even get a wave of nausea. I have actually came home being sick once because I was in the studio all day. So now ever since, i have to eat and drink something and get some fresh air.
I go through phases of this. Low blood pressure is partly to blame in my case, but last summer I was getting light-headed and dizzy really frequently and it was all down to my diet - namely being deficient in iron. In your situation, it doesn't sound as if poor nutrition is the cause, but you could still be low in iron regardless. Low blood sugar is another possibility.