Hello. Don't panic! Many, many of us have been in the same place as you. That said, I do understand - it's very difficult to not be scared. There is something very frightening about these letters!
So, here's the deal: high grade dyskaryosis means that you have some changes in the cells in your cervix which, left untreated, could lead to cancer in the future. In most people, it takes a long time for those changes to progress to cancer. The whole point of cervical screening is to pick up the changes and, although I hate waiting for my letters as much as the next person, I'm very glad that I'm being checked under this programme. It's reassuring that we have access to these services and they absolutely will take care of you. Now they know you have these changes they will want to offer you treatment. This is a great thing! The horrible pre-cancerous cells will be removed and you will be cured. Statistically speaking, this is BY FAR the most likely outcome.
The treatment happens in hospital. You have to go to a clinic. The doc/nurse will talk to you about your smear result and explain in more detail what they found (e.g. for me I had a high grade smear but the doc explained I actually had moderate changes). Then you sit on a bed very much like when you have a smear and they put the speculum in. It's very much like a smear but the doc/nurse will put some solution on your cervix and look at it with a microscope - the pre-cancerous cells turn white. When they treat you, they remove them. You are awake, they use a local anesthetic so you can't feel it, and it's quick. Afterwards you might feel a bit wobbly and not quite right for a few days, and you have a little bit of discharge and bleeding for up to a month.
It's not the nicest but it's sooo much better than being left with the cells inside you.
Six months later you have a smear to double check that all the cells are gone. (That's the stage I'm at.)
So, it's not a nice thing to happen, but most people on here report 'it wasn't as bad as I feared.'
Hope that reassures you a little bit. x