I am so sorry for your loss. There are a few possibilities for the symptoms you describe.
One cause is back pain,and others are seizure or stroke. The eyes going backwards in the head sounds like a seizure. Older dogs can get calcifications of their spinal cord disks. These calcifications, can break off (as cartilage emboli), and circulate in the blood and become lodged at various locations such as spinal nerves, and the brain. They can then cause damage,pain and paralysis. A piece could also theoretically end up in the brain causing a stroke. Emboli can also travel to the heart, so heart attack is also possible.
I am certain that you did not do the damage by lifting him.
HI Dr. Aleda. Thanks for your reply. I appreciate your help.I keep going over and over in my mind trying to realized what i did wrong.
Are seizures painful? was he screaming because the seizure? because he was in pain?
I spent 16 years making sure he was happy and the last hours i could not do anything to aleviate his suffering.
Thanks