My heart pumps so fast and feel that my throat narrows that im grasping for air when lying down

Im at week 19. My heart pumps so fast and feel that my throat narrows that im grasping for air when lying down. I would try to sit back up or turn my body to left or right to see if it helps with slow and deep breathing technique to calm my heart. This happens quite frequent, mostly at night, a couple of times in the afternoon when i lie down on my back on sofa. Anyone experience this? I googled and many says this is quite normal. I will be informing gynae about this on my next appt. I went GP, doc also asked me if I feel stress, i dont even feel stressful at all. Rather I feel very relief with a supportive, involving and caring husband, helping me throughout my pregnancy until now.