I Have Had Dizziness Every Morning Upon Waking For The

I have had dizziness every morning upon waking for the past two weeks. I stand up and walk very carefully and have only fallen once. The dizziness lasts about 1-2 hours. My blood pressure is about 125/75 upon waking and 135/80 in the afternoon. My oxygen is 93-97%. I am a 78 year old man in in excellent health, nearly vegetarian, exercising every day (30 min strength, 1 hr bicycling, plus some hiking, skiing and baby sitting). What could be wrong?