My baby peach-face died

Question
I am so devastated as my fiance found my little bubba,
Kipper dead in his cage this morning. We only got him on
saturday (3 and a bit days ago) and he's about 8 weeks old.
Last night he showing weird signs. When I went to put him to
bed in his little hut, he was already asleep in the corner
of his cage so I gently picked him up to put him in his hut
before putting the cover over his cage. However, when I went
to pick him up, his legs and body seemed really
straight/stretched out and stiff and his feet where all
curled up. I noticed something was wrong straight away as
the feeling of picking him up was totally different from
other times. Without wanting him to wake up, although he did
in the end, I put him in his little 'hut' (just a blanket on
the floor of the cage that has a little opening - he has
slept in this for the past 3 nights) when i put him down he
fell over. Although it seemed like he was awake and
conscious, he tried to walk in his hut on his legs but couldn't balance and his feet were still curled up! I
started crying as I freaked out about what was happening.
This went on for a couple of minutes so i just put him
against my chest under my pyjama top as he loved cuddling
with me this way. After about half an hour he woke himself
up and was perching on my finger as usual and feet were
fine. I put him back into his cage and kept the blanket over
because at this stage it was about 11pm and I wanted him to
go back to bed. I was up for another 15mins after putting
him to bed and the whole time he was still awake climbing
all over the cage perching on his branches etc. I had
thought maybe the 'paralysed like' feet/legs he was showing
was just because he was in a deep sleep and possible sleep
"walking"??
Anyway, before I went to bed I just peaked under the cover
and said something like "go to sleep kipper, goodnight" he
seemed very eager to want to be near me at this point as he
was on the other side of his cage and flew right to me. I
said something like "no i cant hold you now you have to back
to sleep" after a couple of seconds i was still watching him
and he realised i wasnt going to get him out so he started
walking off doing his usual thing but i noticed he was still
walking weird. His feet where fine at this point -it was
more his body which was on a slant and his head was on a
tilt to the side. I just thought he was doing this because
it was dark under the cover and he was just trying to see
where he was going. This worried me but I made myself not
get any more concerned than I was from the first scare.....
That's when my fiance found him dead in the corner of the
cage with his beak leaning against the bars like what he
does when wanting to come out of the cage. One wing was half
out, his eyes were half closed and one foot was curled up. I
do not deal with animal deaths at all and completely lost
it. I have no idea what I have done wrong or what happened
to little Kipper over night.

Answer
- I'm deeply sorry for your loss.  I truly understand how hard this is for you.   

To help me be clear about this, Kipper had only lived with you for a few days?   

Where did he come from and what was it like there (where he came from)?

What did they feed him?  What did you feed him?

Had anyone been cooking in the house where Kipper was?  How about using hair dryers, blow dryers, curling irons, toaster ovens, candles, air fresheners, any sprays at all for anything?

 This additional information may help, but no one can ever know for sure without a necropsy being done.  Even then, sometimes an underlying cause is never found.

Let's try though.