I have been feeling the same. I asked my doctor why this could be happening because I thought it could be due to low blood pressure. The doctor said it is normal and most felt during the 2ND trimester. Since the baby is growing more quickly the baby is taking more nutrients from you & the blood flow is more concentrated to the areas where your baby is; you're getting less blood flow to your head & other needed areas. That's why you'll feel dizzy. Drink lots of fluids, it'll help. 😊
When that happens to me I drink ice water and maybe a small square or two of chocolate to get my blood sugar workin and then I'll eat once I feel "stable".
That happens to me a couple times. Could mean you need to eat something, drink some water, or just all the extra blood flowing through your body. That's what my dr told me. But if it continues regularly, call your dr.