My heart rate suddenly go so fast (about 180bpm) after l yawn and l think my lung pressed against my heart when yawning cause my heart to beat fast. It has already over 2 hours. My heart rate always normal but sometimes when l yawn, burp or laugh then my heart rate will go fast for few minutes then go back to normal.

it sounds fairly normal as everyones heart rate changes depending what they are doing. but 180 after yawnin does not sound right. im not a proffesional or anything but it dont sound normal. just go 2 your doctor and get it checked out to be on the safe side
hope l helped

True. Your heart rate will also go down if you move your neck around a bit with a gentle stretch. All of these effects are just momentary.

Yep, that is normal. When your lungs are expanded, it limits the amount your heart can contract, then your heart thumps a little more to catch up.