Gruesome

A schematic drawing of the position in which an amateur cave explorer was trapped for 27 hours (until he died).

The full incident report is recorded at the National Speological Society News of October 2011 (scroll down to page 15 re John Jones at Nutty Putty Cave).

On the evening of November 24th, John Jones (26) and ten of his

family members including children entered Nutty Putty Cave

and toured the entrance area. After a short time, most of the

group left while John and others including his brother Josh

continued to explore. They proceeded to a tight, nasty, passage

known as Bob’s Push. This passage is mostly belly-crawl size

and undulates up and down before taking a decisive turn to the

left and downward. The remainder of the passage to its dead-end

is very tight and slopes downward at about a 60-degree angle.

John entered the passage head-first and continued head-first at

least 30 feet down the steep, tight section. At some point, he

realized he could not back out against the force of gravity. John

sent the others out of the passage and continued downward,

hoping to find a place to turn around...

Death by positional asphyxia can occur from prolonged inversion without any other injuries (cf. Saint Peter).  There are multiple documentary videos about this incident, including this one (hat tip to reader drabkikker, who located it).  The embedded schematic is a screencap from this one.