Unless Sqad is around it's unlikely that anyone here will have the expertise to provide a definitive answer. (I suspect that even Sqad wouldn't be able to give you such an answer anyway without being able to give you some tests).
I've also been doing a bit of googling and the symptoms you describe do seem to match up with lactic acidosis. e.g. see here:
http://www.nhs.uk/Conditions/Hepatitis-B/Pages/Treatment.aspx
However, without the need for any googling at all, it seems obvious to me that they also matchup with countless other things (e.g. 'flu or even a hangover!).
As I read it, you're not going to drop dead between now and when your GP's surgery opens in the morning. So try to get some sleep but set your alarm so that you can phone as soon as they open (or, better still, walk through their doors at that time). Tell the receptionist that you're concerned that you might be seriously ill and insist on seeing a GP (
any GP, not necessarily your own) as soon as possible.