Baby movements

So yesterday I went to the hospital as told by midwife due to babys reduced movements, he hardly moved when we was there he done two big movements and they were happy but they noticed every time he moves my heart rate drops, does anyone know why this might be?? they didnt explain why they just said it shouldnt be doing that

plus note today hes moving none stop and I can feel hill moving his head down in my pelvis and ot feels extremely wierd and uncomfortable