There are many things to consider when looking at lightheadedness/dizziness. It is not uncommon to experience lightheadedness from time to time. You may be experiencing orthostatic hypotension, which is a momentary drop in blood pressure when changing positions (lying to sitting, sitting to standing) to quickly. Even though your blood pressure is fairly normal, one thing to consider was your blood pressure 140-150s/70's before, then dropped to the 127/77? If that was the case then you may be experiencing the side effects of orthostatic hypotension.
If it is not your blood pressure, there are other things to consider for causes of lightheadedness/dizziness. For examples, dehydration, medications, vertigo, allergies, illness, a common cold, anxiety, stress, etc. You can read more about dizziness/lightheadedness at the following link: Dizziness
Thank you Tara. My blood pressure has never been that high (in the 140-150's/70). Actually its usually around 120/70, which indicates very little change. Dehydration and stress definitely stand out as possibilities so I'll look at those. Thanks again for your response.