my 13yr old jack has started to faint on waking [only after a long sleep usualy mornings] particulaly if warm,although we do try and have a fan on him betwen faints he is normal recovering in seconds.a bllod curve told us his diabetes is well controled and several exams have proved nothing he is on vivitonin wich has made no difference if anything it may have made it worse has anyone got any ideas.

Don't want to alarm you, but my SBT fainted a couple of times last year and we couldn't find anything wrong with him.  Both times were when we had returned home and he had obviously jumped up to greet us from being fast asleep.  Last July he collapsed.  He had an enlarged spleen, which had been leaking blood and was extreamly anemic.  Luckily we got him to the vets in time and he has made a full recovery. It may not have been linked, as the faints were quite a while before the collapse, but I personally think these were early warning signs.  I hope Jack's problem isn't as serious as this, but you could ask your vet to check his spleen isn't enlarged, they can do this by feeling the abdomen initially or by doing a scan.

Hope this helps.