Yields on bonds go up when when bond price goes down. You can think of it this way: Tesla bond would have to pay 8% for investors just to be on par (break even), given the current interest rate regime. Of course, bond pays the fixed rate agreed at the issuance, so if you are bondholder, your bond is now worth less, and - if you sell it now - you realize the loss. Put another way, if Tesla to issue new bonds, they have to issue them _at least_ with 8% coupon, because investors will demand premium for risk.