I wonder if his heart had every been checked out?
Being sweaty (while sleeping or eating) can be a sign of a heart problem (as can extreme fatigue and poor weight gain).
Unfortunately heart defects are the number 1 birth defect and 2/3 of the time are NOT diagnosed at birth. 80% of undiagnosed heart kids die before thier FIRST birthday.
My son has Tetralogy of Fallot so I've learned a LOT in the last two years about heart defects and it amazes me that it is not mandated for every hopsital/ped to test for heart issues at birth. All they have to do is put that little red light clippy thing on the child's toe for a few seconds to get a read out of the oxygen level in their blood. It is non-invasive, doesn't hurt and is easy to do.
Anyway...because of my knowledge of heart related stuff...it does make me wonder...
In any case i'm deeply deeply deeeeeeply sorry for your loss