Although that was probably just from getting up too fast, there are other reasons why pregnant women feel dizzy. This article explains what you can do to minimize this problem:
Not enough food and drink When you don't eat enough, you can end up with low blood sugar (hypoglycemia), which can make you feel dizzy or faint. This can happen much more easily when you're pregnant.
Dehydration can have a similar affect. Make sure you stay well hydrated by drinking eight to ten glasses of water a day — more if you're exercising or if it's hot.
Try to keep your blood sugar from getting too low by eating small, frequent meals during the day instead of three large ones. Carry healthy snacks so you can eat when you get hungry.
Anemia If you're anemic, you have fewer red blood cells to carry oxygen to your brain and other organs, which can leave you feeling lightheaded. Iron deficiency is the most common cause of anemia, so be sure to eat an iron-rich diet and take a prenatal vitamin with iron, especially in your second and third trimesters. If you become anemic, your caregiver will probably prescribe a separate iron supplement as well.
Getting overheated Spending time in a very hot room or taking a hot bath or shower can cause your blood vessels to dilate, lowering your blood pressure and making you woozy.
If you feel dizzy when you get too hot, avoid stuffy crowded places and dress in layers so you can shed clothes as necessary. Take warm showers or baths instead of hot ones, and try to keep the bathroom cool.
Hyperventilation Excessive exercise or anxiety can sometimes cause you to hyperventilate and feel faint. Although exercise can help your circulation, be careful not to overdo it if you're feeling tired or not well. Start out slowly. If you start to feel lightheaded or dizzy while exercising, stop and lie down.
Vasovagal syncope Some people get dizzy when they strain to cough, pee, or have a bowel movement. These actions can prompt a vasovagal response (that is, an effect on your circulatory system by your vagus nerve) — a decrease in blood pressure and heart rate, leading to dizziness and fainting. (The word syncope means fainting.)
Dehydration, anxiety, and pain can also trigger this type of reaction, and pregnant women are more vulnerable to it. Lightheadedness and warning signs such as a feeling of warmth, paleness, sweating, nausea, yawning, and hyperventilation often precede vasovagal syncope. Pay attention to these signs and lie down immediately to help keep yourself from fainting.