After I Went To Yoga Yesterday, I Experienced Mild Dizziness.

After I went to yoga yesterday, I experienced mild dizziness. The symptoms have continued today. The problem in today's yoga class began whenever I put my head down towards the floor [like in standing front fold position]. I was okay in this position as long as I kept my head up. I will drink more water. I want to know how long the symptoms last before I have to go to a doctor.