Hi Dietcoke, we crossposted there.
Sorry to hear you've been ill. Glad you're having a nice weekend to make up for it though.
Thoughts about your ds and getting dress are:
a) does he wear different clothes at the weekend than he does for nursery at all?
and
b) I know it seems odd and hard to fathom, but he probably can do some things sometimes, even though they bother him - whereas on other days he is already too full up of other stresses and sensory stuff and it becomes too much, so he can't do the same things on those days.
At the weekend, there's no stress, he has all the security of Mum and Dad and home, with no pressure or having to run to a timetable or schedule, so his anxiety levels are low and he can cope with doing things that he might otherwise struggle with or doesn't like, because he's not already overloaded.
In the week, he has to get to nursery by a certain time, he knows there will be noise, smells, other children, different rules and he will have to be social and interact with different people and children, so his anxiety levels are up before he even leaves the house. Even if he enjoys it when he gets there he will still be aware of all the 'stresses' that it places on him.
Ds1's inclusion teacher explained it to me really well actually. She said to think of it as, all people have a bucket for their anxiety to go in. An nt person's bucket has maybe a bit in the bottom or is perhaps half to threw-quarters full when they are under stress or pressure, but children with ASD and similar problems have a bucket that is permanently filled to just below the brim, so it doesn't take much for it to overflow. Overflow can result in melt-down, non-compliance, anxiety based behaviour such as tic-ing and also increase their sensory problems (heightened anxiety = heightened sensitivity).
Re the fainting - the weird thing is its actually lovely and cool in my kitchen. The oven has only been on low, as I'm doing madeira's which you have to cook slowly on a low heat and we have he windows open at the front and back of the house so there's a lovely breeze.
It feels a bit like it could be low blood pressure. The seeing stars and blood draining from extremeties seems to back that up and I sort of feels like its blood-pressure related as well, if that's even possible. 
It just happened again when I went to turn the paste ears and tail I have drying in the kitchen. Fortunately I was ready for it this time and made sure I sat down before I fell!