Alamak, I totally get that scary feeling, a few of us went through similar things in the third trimester, and it's quite common sebab the baby dah besar and pushes everything around, including your lungs and diaphragm. Try propping yourself up with extra pillows so you're not fully lying flat (semi-reclined position helps), and see if sitting upright or standing for a bit gives you relief; some of my mum friends swear by doing gentle stretches or just changing position frequently throughout the day. That said, sebab you're feeling this quite a bit, I'd really suggest checking in with your doctor or midwife at your next visit or even sooner, just to make sure it's nothing else and get proper reassurance, especially if it's making you anxious. Jangan worry lah, but better safe than sorry kan!