I Feel Dizzy For 3-4 Seconds Every Morning After I

I feel dizzy for 3-4 seconds every morning after I wake up and slowly sitting on my bed. And at nightime after I lay down in my bed for 10-20 seconds, I feel dizzy for 3-4 seconds too. I've been monitoring my blood pressure every morning and night and it averages 128/82 and my heart rate is 69. So what disease do I have, Doctor?