It can be draining and exhausting but I think the majority of its to do with will power. I know when I changed several years back to more of a labour position compared to the office desk position, my body was wrecked but my mind was still active enough to want to do something else after work.
However, that said, being a fulltime mother and being drained mentally by the time I put my daughter to bed, still manage to find the energy to come downstairs, grab a coffee and then sit building an app and debugging SQL errors like last night...
Willpower and determination, work-life balance.
I would suggest setting a few nights a week e.g mon-wed focus only and then thurs-sun relax in evenings. Once you have done this a few weeks, your body and mind will adjust to it and think its normal and then you won't feel like it's such a drain on you mentally.
Hot shower can help but I find its a 50/50, somenights makes me feel tired and other nights, also listening to a podcast on web development and keep me aawake enoughto want to do something.
Let me know how it goes ;)