What Causes Light Headedness And Dizziness While Trying To Get Up Quickly?

if I get up quickly i go light headed and dizzy. I have checked my blood pressure and it is 113/63 60 pulse. I am 42, 6ft 1.2, 16 stone 2.6lbs, was 30% bodyfat, now 21% and have lost 32lbs in the last 12weeks on the thomson diet and supervision from my Gym trainer.8 min warm up on cross trainer, 40mins resistance weight training and 500m cool down on concept 2 rower. Is this blood pressure ok?