In the second sinking, when H.L. Hunley, himself stuck the bow of the Hunley down into the mud of Charleston Harbor (and, forgot to close his forward ballast fill valve) the bodies of the panicked crew were found clustered around the (un-openable) aft access hatch.
The point was, the final crew showed no signs of panic or distress due to asphyxiation or drowning, etc.
Death could have been instantaneous, and I hope it was. Or death could have been slow and agonizing, as the sailors waited to suffocate at their stations (the only place they could sit down).
The second sinking was different. Nose down with valve open, the stern would have an air bubble as the sub filled up. You would expect everyone crowded aft.