I watched a tv special some time ago that discussed this, and what exactly Jesus died of.
Their best guess was the combination of the trauma, the falls with the cross, and the crucifixion all played a part. The wounds and loss of blood weakened Him. With the falls, they guessed that He may have fallen so hard that it caused heart damage and begun massive buildup of clear fluid around His heart. And the crucifixion would increase this, and also cause more trauma to His heart and lungs. Finally when He was about to die, they said that He would have been aware of His death because He could feel His heart about to stop from the pressure. That it would have started to slow and then stop.
This would also explain the blood and water from the wound in His side. The soldier’s lance piercing the heart and blood and the clear fluid (water) flowing out. It would have flowed out pretty strongly since it was pressurized.
Again, it was their best medical guess.