Apologies for vanishing, I've been staying at my Mum's to look after as she's just had a hip replacement, healthy lot we are ! Sorry to hear they haven't sorted out his insulin but as the others have said, the insulin pushes his blood sugar down. If they give too much they will push it down too far and he will have what is known as a "hypo" where he will start to act strangely and become disorientated. As mentioned stress can push the levels up. I'm sure they will sort it out very soon but I think unfortunetly it's a matter of trial and error to some extent to see how much lower each unit of insulin will push his blood sugar.
Things now are so much easier for my DH than when he was a child. He takes something called Lantus which is a long acting insulin and controls his blood sugar levels throughout the day and night to keep them stable (within the ranges of levels in a non-diabetic person. Then if he eats something, he gives himself some "short-acting" insulin to deal with the increase in blood sugar that the food produces. He's found that works really well for him. Obviously as his immune system is suppressed he is a bit more prone to catching things that are going round but not horrendously so by any means. He's grown up with this being part of his life and it's become automatic for him. I don't think it's stopped him doing anything that he wants to and certainly hasn't held him back academically or professionally (he's got a couple of degrees and is the technical director of a fairly high profile small company).
He goes for regualar check ups with the hospital and seems absoutely fine. He did once have a little bit of laser treatment on the back of his eye, but that's fine and they keep a close check on it. He's been put on tablets to keep his cholestrol down, not because it is high but because recent research has shown that taking these as a preventative measure does help reduce the risk of damage.
I've known him for 9 years now and have become good at reading the signs for when he goes low, which have been really rare in the last few years since he changed to Lantus. The only time recently I cocked up was when friends were down (2 nurses) and there was an alcohol related incident which I won't relate in detail, suffice to say that myself (medically related background) and friends were rather red faced in the morning as we really should have known better and we can never return to a certain Chinese in our local town
Try not to focus on all the possible side effects that you will read about on the net. As other's have said, there is so much research going on and progress made that 10 years down the line I am confident that diabetes will be seen in very different terms. Be informed so that you can make sure that his control is as good as it possibly can be as basically this will help prevent the complications that can occur, but don't panic if it takes a bit of time to stablise his blood sugar intitally. For the minute the main thing for the hospital to do is to get his blood sugar levels stable and you all used to the new routine. Reassure him that he will still be able to do the things he wants to do, maybe with more supervision or in a slightly different way for the moment. Have a word with the hospital, I would guess that there are some good books aimed at his age group who have just been recently diagnosed (if by any chance there aren't I'm sure we can write one for him and there must be an artistic MNetter around who can illustrate it for him.) Apologies for the length. I have my fingers crossed that he gets home to you for Christmas.I know it's different, but I have a 6 year old who was diagnosed with dyspraxia & hypermobility a year or so ago and I remember how I felt when I got propelled into a world of hospital abbreviations and doctors. Please CAT me if I can help in anyway.