Are there any historic reasons that may justify your stressing about work related issues? e.g. Have you made a mistake in the past that has had a significant impact upon you, your employer, or a customer? If yes then a reduced self belief is understandable, (i.e. you now more frequently see the "Glass-Half-Empty".) . If no, then maybe a bit more of a positive "Glass-Half-Full" attitude may help. If you have 8years under your belt, with no major ****-ups along the way, then you have probably grasped the basics, gained some real world experience and now have a few years of knowledge to work with when encountering unexpected eventualities on a job.
If you are running your own business, or are in some level of management or supervisory role over other colleagues/employees, then I would think there is always an element of planning or evaluating tomorrows jobs whilst not at work. But providing you can keep a measure of importance over all tasks and priorities, it is not much different to a working parent thinking about things they need to organise for their children whilst at work for when they get home. [Don't forget family commitments and relationships last a lifetime, employment stops a lot sooner! Keep a reality check on priorities].
I think the biggest stress and out of hours anxiety comes when you have an employer who is demanding every last morsel of flesh, out of every working day, with no tolerance to normal everyday human personal needs, and flexibility to give a bit of trust and leeway that employees are happy to work-hard and play-hard. The modern technological era of instant communications by mobile phones, vehicle tracking devices, spread-sheet analysis of every job from quotation to commencement to completion to payment, and progress targets based on previous work has crushed the lifeblood and motivation out of vast swathes of employees in numerous industries.
I remember an era before mobile phones or pagers, where if you disappeared off-the-radar for half an hour, or three quarters of an hour, between jobs to "do a few personal tasks", it didn't raise an eyebrow or generate any stress to anyone in the company. Providing the job was done within a reasonable timescale & costs were +/- a not-to-over-the-top-percentage, of the quoted figures of the sales staff, then all was good in the world and the pub ironed out any bits that weren't!
Are you just working alone or does this relate to your previous thread, (May 8th), about added responsibility that you don't want?
Doc H.
