Lethargic Cornish Rock/Meat Bird Issue

Good morning! I've been reading through your website trying to find an answer to, "Cornish rock sleeping illness?" I've been raising chickens forever, but this is my first go round with meat birds. I have ONE, now two birds this morning, that seem to be very lethargic, won't eat or drink anymore, but do wake up when I touch or pick them up. I am honestly freaking out (says the 50 year old woman who thought she knew "chickens.") I am truly at a loss and no one seems to be able to explain what this is. They are 5 weeks old yesterday. The first one is still alive, but is going on day 4 with no food or water. AND we live in Arizona where our daily temps are reaching high 80's. They are housed in a large caged open air pen (30x40). I separated the sick/sleepy one as soon as I noticed thinking it may be disease, but I'm pretty sure that isn't the issue. I also checked her for any insect bites/stings although I've never seen a chicken get stung by a scorpion. I don't want to put her down if this is something she can bounce back from? ANY thoughts at this point would be SOOOO appreciated. Thank you

How old are they?  Are they getting near the time they'd normally be killed for meat?

I found that when they reach that weight, their legs generally give out and they'll suffer more and more with pain in them and not want to stand up.  I managed to keep one female alive by keeping her on starvation rations and only allowing her to eat what she could catch over the summer, which made her run around and keep fit.  But even so she eventually got too big to stand. We did get a few eggs from her though and managed to raise a few of her chicks, crossed with a Light Sussex, which were much, much less heartbreaking to raise.

Here's a long thread about the joys and sorrows of raising cornish cross/rock - making the best of raising cornish rock cross

They are only 5 weeks old so not too large to be in distress I would think. But again, I am obviously in the dark with these guys... we have friends that have processed these before and said  between 8-10 wks is when their time is up so they don't hurt themselves or suffer from weight issues.

I had heard after 4 weeks they start breaking legs and having heart attacks. Maybe this is under factory conditions where they do little besides eating.

Commercially, they are fed ad-lib for 39 days to get them to slaughter weight.  Five weeks sounds pretty close to that, and was the age when we started losing our first batch of them, one by one, with leg and heart troubles.  

Are they showing any signs of paralysis in any legs or wings? If so, it could be botulism.

If not, I'd assume they're just getting close to slaughter age and are beginning to have joint or other skeletal pain from all the extra weight. Time to eat them!

There is a disease which the locals call "sleeping sickness" in poultry here.  I am not sure what it is in scientific English language.  It has never affected my flock.  But I have seen it and it just looks like a sleepy, lethargic chicken with no other obvious symptoms, and seems to especially effect juveniles.  But I rather suspect that's a tropical disease unique to Africa.  More likely you maybe dealing with meat birds that have already reached their expiry date.  I read somewhere that their body mass outstrips their heart capacity, and that leads to lethargy and all the typical symptoms of heart failure.