There's a temporary blackout whenever i stand up from lying down. it's happening more frequently. is this a bad sign? im scared..

Well, it's not good: Feeling lightheaded when changing positions from laying down to sitting or from sitting to standing may be due to orthostatic (or postural) hypotension. Check out http://www.mayoclinic.org/diseases-conditions/orthostatic-hypotension/basics/definition/con-20031255. Drink enough fluids (water) to make urine pale. See your FamilyDoc for evaluation if symptoms persists despite adequate hydration.

Postural Hypotension: I understand your scared feeling. “temporary blackout whenever I stand up from lying down” is due to temporary low Oxygen and temporary Low Blood Pressure. It is called Postural Hypotension. Slowly get up from lying down ;and then slowly stand up Discuss with your Physician for frequent occurrences..