how long should you be dizzy from standing up too fast?

To add to the question, I woke up today super swollen which I know can be perfectly normal but I'm more swollen than I have been yet. I don't have ankles anymore. I've been dealing with dizziness the past couple of weeks, and was even put on medicine to take as needed for it. I've been resting all day, taking naps when I felt like it and just generally lying around keeping my feet up and drinking tons of water. I'm still extremely swollen and just generally feeling weak and shaky. My blood pressure has been perfect my entire pregnancy but I have had low iron which eventually went back up and I was taken off of my iron supplements. About an hour ago I stood up to let my dog out and got extremely dizzy. After I let her out I went back to lay down and have just been extremely dizzy. Almost like sea sick or like you just got off of a dizzying roller coaster. I can hardly roll over in bed right now and won't dare get up to walk until my fiancé gets home from work. Is this just normal third trimester things? Should I be concerned and call my doctor?