Lots of things! Sorting out the significance of those symptoms depends on accompanied circumstances (precipitating events, duration, palpitations), objective findings (abnormal cardiac or neurologic exam), age (younger, older), etc. Often these may be relatively benign (if younger patient and not objective abnormalities), but may also be a harbinger of more serious underlying conditions. Talk to your doctor.
Vertigo. If drug side effect is excluded, far more common cause of feeling of one or more of lightheadedness, spinning, tilting, falling, losing balance is vertigo. Diagnostic difficulty occurs when symptoms are mild. Expensive cardiac work up is often done. Many a times some cardiac abnormality e.G bradycardia or severe carotid stenosis is found and treated but dizziness persists until vertigo is treated.
What can cause dizziness, lightheadedness, and headaches? I know I'm not pregnant. I missed my period last Month and I don't have any ear pain.
Dizziness. If you are sexually active & missed your period make sure 1st that you are not pregnant. There are so many causes for dizziness. You need to see your Dr for evaluation & work up. Good luck.
Numerous. Many, many, many possible causes. It is far to complex a subject to answer in this limited forum. Best to discuss with your doctor.
Not enough info. Need more information to figure this out. What makes it better or worse? Have you seen a doctor about this yet?
Vomiting. Vertigo is the sensation of movement when you are not moving. For most people this causes nausea and vomiting. The sensation comes from ear and brain centers that are designed for balance and orientation. When they are off kilter we sense movement and get very disoriented. The cause may be quite complex. A thorough evaluation would be appropriate.
Migraine-associated vertigo, can this cause severe lightheadedness as opposed to actual spinning or dizziness?
Sure it can. While the most traditional & specific definition of what is known as vertiginous migraine or as you say "Migraine-associated vertigo" is that of actual vertiginous sensations or spinning/whirling/tumbling/moving feeling either followed by or preceded by migraine headaches there's nothing that says that a person couldn't simply have an event of lightheadedness or disconnected feeling & headaches.
Not usually. Dizziness/lightheadedness is very non-specific and can be seen in almost any disease and can be just be the manifestation of benign positional vertigo. Hypothyroidism normally doesn't present with that.