usage of the verb, to regress

[hardworker]

Thank you Alan for your comment on my post in the grammar help forum.

I have recently learned a new word, to regress, but I did not use it correctly in that post. I would like to try again and learn how to use it correctly.

Longman Dictionary states that to regress means to go back to an earlier and worse condition.

I would like to use it in a sentence.

(ex) Last year, Mark worked very hard to improve his grade average from a C to a B standing. This year, he is regressing to the lower grade average because he is not working as hard.

Am I using the verb, to regress, correctly? Please help me learn how to use it correctly. Thank you very much.

[knowable]

You can say his grades have regressed.

E.g., Last year Mark worked very hard at school and his grades rose from C to B. But this year, his grades have regressed as he has stopped working hard.

I have to say I am not certain regress is a suitable word here though. We know regress means to return/go back/relapse/revert to a former state. And I have heard the word being used to describe stock market performance. Other instances where you are likely to hear the word being used is in describing behaviour or health condition.

E.g., a person had been ill for a long time, then for a while he/she showed some improvement only for their condition to relapse. Therefore, we could say that person has regressed or their condition has.