You can mediate lying down standing up, sitting on a chair, however, you can comfortably do so. There are absolutely no reasons whatsoever for you to do mediating lying down.
I actually do meditate lying down! You just don’t want to do it on your bed. Lay on your back, spread out your arms and legs, open your palms, and empty your mind. I recommend playing Indian flute music, soft classical music, or rain sounds. Breathe deep and be still. RELAX!