Last night I took a sleeping tablet at 10.30pm...

Was it a prescription tablet or Nytol etc.?

I have been prescribed Zopiclone before and TBH I was zonked out for most of the next day!

It was just a Nytol one-a-night, said to take 30 mins before bed etc. I still feel like I'm walking round inside a fluffy could that just wants me to fall back to sleep...

I don't think I'll 'knock myself out' with one of these the night before the wedding or I'll be a zombie bride!

I have visions of you acting like the dad in Father of the Bride II when he takes sleeping tablets. ?

I have never taken sleeping tablets so I can't help, but EF's suggested seems like a good idea.

I was like the man in Father of the Bride!

I set some work going and went home again because I was just not 'with it', I drank a pint of water and feel asleep for two solid hours (I can never do this during the day normally). I woke up, had another pint of water, ate some lunch and came back to work. I feel like a have a functioning brain now, still tired, but I can concentrate a lot better.

If I ever feel the need for a good night's sleep, I'll just take half a tablet!

That sounds like the kind of next-day grogginess where your body is clearly asking for more rest. Some sleeping tablets can leave you feeling drowsy for quite a while after waking, and the effect can vary depending on the medication and dose. I’d check the leaflet for the specific tablet and avoid driving or anything requiring sharp concentration until you feel fully awake. It’s interesting how even simple measurements require the right conditions and consistency, which is something I’ve come across when looking at digital durometer shore a testing for rubber and elastomer materials. In this case, though, I’d definitely give the body some time to properly wake up.