why is my heart pounding ?

like a fast heart rate not too fast but a like nervous pound.?? i didn’t do anything extreme today just worked out and drank a protein shake which i always do . I do feel alittle dehydrated.... i drank a water bottle already. It’s not my anxiety either because i know the difference in my heart rate.. i just feel like i’m outta breathe or soemthing. .. i can breathe good