Thanks everyone for your replies. Just to clarify one point, I haven't fallen ill (at least one good thing) and 'the body response' wasn't the illness, it's more of some mental block. I just can't make myself do more work on this phd at the moment. Also just to be very practical, is there any way to wrap up the 4.5 years into some suitable line on the resume/CV if I don't have a diploma after?

It's something everybody thinks time to time on their phd journey. Probably very little number actually is doing it. It's probably just a dream of many phd students similar to how some hard working employee may want to quit his job and move to his dream destination.
I've started my PhD degree in April 2006. I was fresh, somewhat interested in the topic and thought it'd be good to get a PhD degree before I go off to work. The university was kind enough to offer me a scholarship. The research facilities for this topic were also the best for Europe which is a big advantage. Everything seemed nice, the sun was shining and I was spending days in the lab. I've had lots of ambitions to submit to conferences even though the research was not yet up to the level, many hopes (lots of fear to fail too). In the second year it was a major slow down, between 2nd and 3rd I've been toying with idea to quit, but having nothing better to do made me stay in 3rd. I've done a little progress then. When the 4rth year came, my 3 years funding was over, I've moved away to save money for housing and living costs. Actually I moved in with my long-distance partner, which meant moving to a new country. Things went great in my relationship, things went downhill in my PhD. Now it's 4.5 years into it (PhD) and nothing has been moving. It's mainly my fault. I'm probably over reacting, but I can't find any way to force myself to get to work on it again. It's more of a body response when you had too much of something.
In the same time, after having been called a 'PhD student' for so many years, I feel like it became a part of my identity, of who I am. Having spent years in academic community where Mphil is considered to be a failed PhD I find it difficult to ask for one instead of battling over PhD without any hope for progress in it (I'm myself fully to blame of course).

Can one just quit it? Is it a reality and not things of legends? :) What do people write on their resume then to justify the years spent doing what is basically a research? I'm sure that there are skills I'm taking with me from it... even without this degree and I'm not sure I need this degree anymore.

Any advice/comments and suggestions are appreciated.

The situation is very familiar, the further I was getting into my fully funded PhD, the more I had some kind of allergy against all things connected to it. In the end I couldn't tolerate it anymore at all. Currently I've moved away to so call 'write up' and 'finishing off active research work'. Being in a new country I found thousands of excuses not to get to it. I believe I have worked only during the first week. My partner has been trying to push me to do it, but even he gave up on it as it didn't change much. I think the motivation to finish it should come from within. Now I'm in frond of similar dilemma - I want to quit, but without some kind of paper justifying all these years spent on PhD I will be a bad job candidate. So it means I've got to go for MPhil... But I've got a Masters already (from a different uni). Also just a thought of going to my department to give an MPhil presentation kills me... You know how all these academics are. If I tell them I want an MPhil it's more of accepting my defeat in some kind of PhD degree competition. I may be pitied and looked down upon. OK, perhaps I can stand it for a day before I leave this environment forever, but ... Again do I need that MPhil really that much? Can't I simply quit and put some line of doing 'Research work' at uni during this time? Would it be correct as an explanation of PhD. It is the research and since it was paid (scholarship) maybe I could call it 'work'?

I've met my supervisor last time and have put the deadline (myself), if I don't do any work by September 1st I'd like to do an Mphil... Now it's September 1st I haven't done any work. So I've got to go for an MPhil... But I would rather quit... Why is it so difficult to decide to cross off this goal even though I've completely lost interest towards it? Why leaving people sometimes went much smoother than quitting a PhD degree?

Anyway, good luck for people who are in front of the same challenge. I hope the decisions come to you easier than they do to me.