I don't know how common it is with panic disorders but I know this "gray" feeling is common to other situations. I used to work piece work. Small short time jobs and then move on to the next. Some of them were very hard and had long days. I worked sometimes ten hours a day seven days a week for two months or more at a time. The only time off was to get more saw gas and groceries. We were always fifty or more miles from the nearest town camped right on the job. I even had an apartment size wash machine and a generator to run it. Work, work, work.
The let down at the end of each job was very bad. Getting motivated to do anything during down time was very difficult. Physically I was fine but mentally I was burnt out. Stumbling around trying to garden and prepare for winter before having to go back to work.
Routine does this. It was worse since the reason for doing piece work was to make quick money and see some fantastic country but the routine turned me into a zombie good for little after. I know of people who can not enjoy their time off because the routine of their job is dragging them down. Their performance at their job is suffering too.
I now know that it calls for an attitude adjustment to break out of this. Pity I didn't know how to do it then. I lost so much time to what can only be called the blues I guess.
I've heard it referred to as house wife syndrome. Same old, same old day after day.