Pounding heart when standing up or climbing stairs

Hey, I am a 17 year old male and recently I have been dealing with an issue. Every time I sit and stand up again or climb stairs my heart starts beating very quickly and strongly. Today I had to sit and stand multiple times in a row and I was feeling so bad and heart was pounding incredibly fast. I also had to climb 2 sets of stairs and I kinda felt like passing out and my heart was beating incredibly fast. I get scary thoughts that this could have possibly damaged my heart. I also do have anxiety disorder but I don't think this happens because of anxiety because it happens no matter how I am feeling. Other symptoms that happen randomly are feeling really cold, tingling hands and feet, lots of back pain. What could this be and how can I fix this. Please help.