Walminskipeas...
I can empathise and I do think the PhD can trigger a mid-life crisis in your twenties. You've never done anything like it and don't really know how you're going to respond to the bumps in the road. The stress and pressure can be so intense, even if you're getting positive feedback from your supervisors and others. But if you accept that you're going to be moody and can get the people around you to accept that too, it is bearable and worth it.
I was writing about a really depressing book and having trouble getting it to work in the larger context of my PhD, it nearly caused me to have a breakdown, partly because of the subject, but more because I couldn't get my head around how to deal with it. The feedback I was getting was 'good, keep going' which is fine but hardly constructive. I did a course on stress prevention and time management offered to PhD students at my university. We were asked to write a paragraph about our most stressful PhD moment. Some very young girl shared with us that her most stressful moment since starting was missing a bus to get to a conference in a city she didn't know well and thus she arrived late and had no chance to pre-network. Aww, I wanted to kill her. My paragraph was turning into a novel about the combined stress from my personal life plus work pressure. The course was useless to me because it was already too late, I was already completely frazzled (and it was stupid--being forced to buy coloured pencils to fill in a chart about how you're going to use your time just didn't help me). This bad time passed though, things got better, then got bad again, then got better. It's a wild ride, and great heights and deep lows are part of it unfortunately. Doing this has made me feel really unstable at times, it can be so irritating to see your motivation and emotions etc be totally destroyed by working too hard or too little, but the point is: you do it to yourself, blah blah, own worst enemy etc.
The others are right, you need to get a few people around you who will listen to you gripe/be supportive/tell you if you're over-reacting etc., it helps to talk to both other academics and non-academics, be they cleaners or artists or whatever. The balance is key. Academics understand some things that others just can't, like how you can be irrational about things you ought to know better than to get crazy about. Non-academics are much wiser about other things. Just bear with yourself. The pay off is worth it, but you shouldn't suffer alone more than you can avoid.
Good Luck!
