What Causes Dizziness, Nausea And Metallic Taste In The Mouth?

I can feel it coming with a flush, slow onset of the following symptoms over 30-90 seconds. I become dizzy, like motion sickness, extreme weakness, metallic taste in my mouth, near or total blackout. I come out of the blackout with nausea, headache, and the nausea lasts for 15 minutes to all day. I am so tired after this happens that I will fall asleep without warning, even while typing. Instantly asleep then realize it and shake myself awake. I stopped driving because of this. first time was 5 years ago and it happened twice in a year, now it happens 2-10 a week. Sometimes 2-3 in a ingle day, then mild nausea for a day or two, then multiple episodes.