Sitting vs laying down BP

which is a better measure of heart health? my sitting BP is so much worse than laying on my back in bed. Often falls into stage 1 hypertension, 130s over 90s. laying down ive had readings as low as 110/75 but its usually around 120/80. High BP runs in my family so im a bit paranoid and I had open heart surgeory within 2 weeks of being born.