What Causes Dizziness Upon Bending?

A week ago I noticed dizziness when bending over (tie shoe to go,for daily walk) and the room spinning when laying down to do floor exercises. I take 25mg hydrachlorathiazide daily. 66 yrs old, 5 5 , 140 lbs Excellent health. Typically my BP is 130/70. I have been monitoring for a week systolic running as low as 106 to 120 and diastolic often at 60 and not much higher than 68. I break my 25mg med in half and take morning and night. I was waking up dizzy as well and have eliminated evening half of med the past few days waking up feeling closer to normal. I will continue to monitor.....should i be more concerned? Thank you, Kathy YYYY@YYYY