Hi, Last Few Days I Am Getting A Feeling Of

Hi, Last few days I am getting a feeling of not being able to catch my breath. I'm not breathing faster than normal, my heart is not working faster. I don't have a history of asthma or anything like that. I'm 37, female, normal weight, no other health conditions. I find it's worse if I lie down, I have to sit up quickly - really unpleasant feeling - like I'm not getting enough oxygen. I try to breathe deeper to get more oxygen in. It goes away by itself after a while but it's really unpleasant.