I'd never thought about this; it was a long time ago. My response is more my thoughts about why (I don't think) anything negative happened rather than why it might have done (first, not second question).
I was still living at home, keeping in touch with my workplace when (later on), I was not job sharing and to some extent, I continued my social life, although I had so little spare time for this. I was still keeping house and providing meals (only for two of us). But I think my normal existence kept me together, even when I had to add to my thesis after my viva.
It will be interesting to read the thoughts of others.
Ndolo - my advice to PhD students is to 'try and keep perspective'. It's a long journey - so a 'marathon and not a sprint'. There will be many highs and lows and all sorts of variations in-between. If a student is really 'struggling' - especially academically (such as writing/analysing) - I advise them to 'take a step back - and have a short break'. If they are struggling mentally/socially - then I usually advise a remission of a few months. PhD students often need a break and respite at various times in their journey - and not be made to feel guilty about it.
Having balanced lifestyle and healthy daily routine that combines diet, sleep, exercise, study, leisure, and many other meaningful and purposeful activities help maintain a healthy body and mind.
Watching the students and graduate students, I noticed that among them is widespread unhealthy food, especially fast food. This is due to the fact that they do not think about the future, strive to live only for today.