Injections

How do I help my 15 year old be OK with needles. My son was getting prepped for his appendix to be removed. He didn't need it in the end however while in hospital they were going to give him drip for fluids. He is so terrified of needles. I told him it's just an instruction and I started the rule of 3 to encourage him to get his hyperventilating under control. His whole body was ridged and he felt like no matter how hard he tried he couldn't relax. He did start to relax while following my instructions after the rule of 3. I was about to start preteaching about the injection when they came in and said his appendix were OK.
Daniel, my son, wants to work on his phobia and he was really disappointed with himself. He wants to be OK if he ever needs treatment.