Anxiety attacks strategies

I have been having a lot of anxity attacks. They occur at random times with no warning. I don’t know why they happen because usually I am just sitting down or talking to a friend, (not doing anything that would provoke anxiety). The only person who can ground me is my friend but I don’t see him a lot. I’m not sure what to do to calm down. Does anyone have any strategies. (A panic attack for me is like hyperventilating/difficulty breathing). I’m currently on a heart rate monitor that alerts me if my heart rate is rising rapidly so I have a general idea if I’m going to have an anxiety attack before it actually begins.