How to I tell my mum I've been having panic attacks if she doesn't understand that kind of thing?

I would probably get her to sit down with me and tell her about what I've been experiencing. Then, maybe you could educate her about what anxiety and panic attacks are, and show her web pages, forums etc. Just what I would do :)

You can always write it in a letter so that you can accurately explain everything but telling her is a good idea.

I went through virtually the same thing with my mum and it didn't help that we have a very weak emotional connection. I believe I'm partially to blame for this because of my tendencies to push people away and be emotionally closed off. The only time I'm ever expressive is through text so you could try looking up an article explaining panic attacks and send the link to her. Another way of trying to explain to her what you're going through is by showing her a YouTube video. There are tons of professionals on the site spreading awareness on mental health so you'll most probably find one that you feel could fully explain the ordeal to her. Best of luck :)

Explain to your mum exactly how your feeling - or take her along to a doctors consultation appointment , so she can hear this from the professionals