What Causes Fluttering Sensation In Throat While Lying Down?

I get this fluttering in my throat, and it feels like my heart is skipping...it happens more when I lay on either side. Not as much on my back and propped up. What is this? I just had my thyroid tested and my TSH was .04 so my dr lowered my synthroid. I am also under some stress and am 52 years old and am having menopausal symptoms.