Your job is probably triggering a fight/flight response constantly.

https://www.health.harvard.edu/staying-healthy/understanding...

Working with your hands and retreating to your shed allows you to sooth / calm rather than getting deeper into those stress hormones.

For me, it also gives time for reflection.

From the BBC: Men's Sheds: 'It's about so much more than making things' -> https://www.bbc.co.uk/news/av/uk-northern-ireland-49615371

Have you read Daniel Pink's When?

He talks about rhythms with most people being morning people - alert in the morning and ready for analytical work, entering a trough in the afternoon, then recovering in the evening. Are you mainly doing your shed work in the afternoon/evening, after work?