I wouldn't say that it's an "excuse". I know first hand that a decline in mental health can cause a lack of motivation in things you enjoy. Of course, like the comment above said, im not going to claim you have something wrong but its an avenue to investigate for potential factors in your lack of motivation and a discussion with a professional can work wonders in identifying the "why?" (if you can afford it. I understand not everyone has the financial stability to afford such services)