I was in the process of changing a flat tire on my truck and I was lifting the spare into position and I couldn't pick it up from a kneeling position so after a minute or two of intense struggle I stood up in a bent over position and finally got the damn thing on. At this point I stood up and that is when it hit me. I started to feel extremely lightheaded and began seeing spots. My heart started racing uncontrollably and I began to feel like I was about to faint. I remembered that I had a two liter of water in the car and I chugged like half of it and finally started to feel a bit normal. I've been feeling lightheaded and been having heart palpitations for the last couple of hours. I checked my blood pressure and it was 143/99 which is high for me. My question is what the fuck is going on?