Jo, this is really an excellent piece of writing. The only error is in the sentence beginning 'It is those moments..'. . This sentence should read either 'It is those moments of pure silence and serenity that I like most of all.' or Those moments of pure silence and serenity are what I like most of all.' Otherwise, it's perfect.

Hello Jo, It's almost perfect! Just a couple of things. I would change this sentence: "It is those moments of pure silence and serenity is what I like most of all" to: "Those moments of pure silence and serenity are what I like most of all" or "It's the moments of pure silence and serenity that I like most of all" I'd make the distinction that it's you who is teaching the class. If you say that you talk in class it sounds like you are the student. You can say "The only time where I have to talk is when I'm teaching a class" and " It has always surprised me how cheerful, outgoing and full of energy I become as soon as I start teaching / as soon as I start my classes" to just make this a bit clearer. Also calling yourself a loner has a lot of negative connotations and implies that you're antisocial so I wasn't sure whether you meant loner. If you wanted to say quiet you could call yourself an introvert or say that you like to spend time on your own. Saying "I'm a bit of a loner" adds some irony and takes the edge off a bit as well! I hope that this helps!