Mephedrone is _not_ your friend, especially if you are as you say addicted to it.
Just to get one thing clear quickly - I'm currently vaguely high on it, I snorted about 150-200mg around 3/4 an hour ago. I've had a bottle of wine too (personally alcohol is far and away my biggest vice and health hazard)
I only use on weekends, and generally I try to stick to fridays (I've got a job, and mephedrone and jobs do not mix well). I now limit myself to 1/2 a gramme or so (though I have done much more than that - see * below).
If you are using _much_ more than this, I'd guess you've got problems. I find complete recovery time for mephedrone (lethargy, general down feeling) is about 4 days, and if you're using more regularly than that you're not withdrawing properly. I'm usally pretty much fully functional less than 12 hours after mephedrone, though I'm normally well asleep at that time. However, like I said before, I still am affected a few days after. The "quick" withdrawal is slowing down and still feeling generally pretty good for up to the next 24 hours or so, well after the high has worn off. The slower withdrawal throws you down a bit for quit a few days after, but you should be still 100% functional... If you're dosing to avoid that secondary withdrawal, you've got problems.
One reason I think Mephedrone is dangerous is an experience I had about a month ago. I spent Saturday out with friends drinking throughout the day, no drugs. I got home (alone) and decided to stay up and go out sunday day, so I did a bit of mephedrone, and a bit more, and a bit more. I went out Sunday about midday. By this time I was hallucinating loads, One of my friends said I was acting weird (I even knew I was at the time). Anyway, I went into town, and somehow got served everywhere I went. I met new people, don't think I annoyed anyone too much, and played pool very badly. Got home about 8pm, went straight to bed since I'd been up for ages, though did put my alarm for next morning.
I got up the next morning feeling a bit rough, but got ready for work, and I got as far as getting in my car before I realised I was in proper _no fit state_ to be driving. I went back into my house, called in sick for monday, and slept almost literally through until tuesday am (I was awake about 3 hours monday night), when I went to work feeling rough as hell... I felt a little crap Wednesday too, by Thursday I was basically ok, and compared to previous few days I felt on top of the world.
The kicker about that day/night/day is this - I worked out how much I drank... It was over 35 pints (confirmed, not boasting). I think I had about 1 1/2 grammes of mephedrone too. I was _completely_ out of control. I'm scared I got served at three different pubs while off my face on Sunday - makes you wonder what you've got to do to not get served.
I used to use cocaine, the only reason I stopped was because I could not afford to get nicked for it again. Cocaine in my opinion is a lot better, and a lot more predictable (if getting from the same suppliers), and a lot less dangerous. I personally advise using cocaine over mephedrone if you can afford and don't mid the risk of getting caught with it.
The first time I did mephedrone I got _really_ black eye sockets, and I got purple elbows and knees, after not doing much at all (about 1/3gramme total). First time users be aware, the physical side effects for first time are a lot more pronounced, so _do not_ do the same as someone who has done mephedrone before, no matter what they say.
I'd also advise not snorting it. It's hugely moreish that way. Personally I buy paracetemol capsules and put it in that, and swallow it (when going out). Make sure you don't put too high doses in when you do this - about 200mg is plenty per pill... the paracetemol is 500mg, and fills up the bottom half of those pills, so a bit under half the larger half (usually white) of those pills should be plenty. At home I usually just mix with water and knock it back (thought tonight I did snort a little). One thing that is already well known about mephedrone is that it will destroy your nose in no time flat if you snort it regularly. It is very very bad on nasal membranes, way way worse than cocaine.
Your symptoms could well be caused by mephedrone overuse, though the only symptoms I've ever had after the high were like previously mentioned, ie. lethargy, slight depression. I'd be very very careful about regular use. I'm pretty sure this drug will screw people up long term, and despite myself being on it now, I do think it should be regulated.
Of all the drugs I've used (which is not many, hash, speed, cocaine, ketamin to name the illegal ones), I believe mephedrone is the most dangerous, because of my own experiences on it. I have never been nearly as out of control on anything else. I've taken more cocaine than was good for me in the past, but I knew what effect it would have, and was basically in control. With mephedrone I've had one major out of control night, and one minor one. It's a difficult drug to manage.
Regarding your unhealthy lifestyle, mephedrone may actually be a gain in terms of heart healthiness because of the strain it puts on it. Mephedrone _does_ exercise the heart, and I know the side effects for other organs are worse than the gain, but I reckon it might just offer a little bit of benefit if your heart is not exercised otherwise.
I can write, can't I?