What is happening to me?! Help!?

Ok, so this recently started happening to me. Say I take a nap, or get up in the morning. When I get up and stand, I feel very lightheaded, weak, and feel like fainting. I black out most of the time too. I also noticed my heart was racing really fast, and I was inside in the ac. I checked my blood sugar this morning and it read 79 (this was before I ate). I asked my mother about it, and she said I could possibly be hypoglycemic, or have really low blood sugar, she asked her friend who is a paramedic and he thinks it's my blood pressure. I haven't seen a doctor yet, but I was wondering if anyone knows what is it. I do eat when I'm supposed to, I don't skip meals, and I'm always drinking something (no, not alcohol). I am very healthy, I don't smoke/drink. This has happened to me 2-3X this week. I am left with a really bad headache and feeling weak/ nauseous.