I just don't understand everything! Why is it that I can change so fast and not even realise? Am I useless now?

Maybe I shall start from the beginning so that you all can better understand what I am talkng about. Today in maths lesson, Mr Hia was teaching on a topic called mensuration. He was teaching on cones, giving us a worksheet to practice on volume and surface area of cones and cylinders. I don't know what happened to me today. I stared at the worksheet as if it was some sort of language that I don't understand.

It took me a bit of time to digest the question and it took me even more time to solve this question, the volume of the cone. I made a careless mistake and my whole answer is wrong. I got the second question wrong too! I mistaken the slice for the cylinder! What has happened to me? I am so worried!

When Mr Hia is going through the surface area of the cone, pie r square + pie r l, then I got confused why the both Rs are different. I don't understand what l is at all until I realised that it is actually the slant height. What has happened to me? I am not like that last time. Why has everything gone blury and I don't understand anything that Mr Hia is talking about?

Since after the holidays, when Mr Hia began the first lesson on maths, I kept on making careless mistakes or misread the question. I very rarely got a whole question correct. I have changed. My maths standard has deproved. I am failing and I don't know what is happening!

Help! Can somebody tell me the answer that I am looking for? I am very frightened about the things around me! I am scared that I will fail my maths! Maths is very important! I really don't know what to do? Can somebody help me?

Joanna