If I can't go to an activity or am to scared to talk to someone how can I stop thinking about me dieing and not being able to think anymore?

It seems as if your talking about anxiety, or a panic attack. Unfortunately there isn't a way to completely get over this fear. You can however try using techniques to get you through it. Breathing is one of them. You may also be prescribed medication to help with the anxiety also.

It seems like you are having an anxiety attack, a good technique to stop it is focus on deep breathing since If you control your breathing, you’re less likely to experience the hyperventilating that can make other symptoms worse. Remind yourself that you are experiencing anxiety, that this is temporary, it will pass, and that you’re OK. Confront your fear in small ways, Start with easier fears or easier situations first, then move up to more difficult ones as you become more successful in confronting your fears. If you get anxious during public speaking, practice in front of a friend or two first. Doing this will give you time to build up your resilience to the anxiety. Remember you are in control of your own mind and life, don't let this thoughts change what you want to do or stopping you from doing something you want.