"Many are now advocating inversion therapy (hanging upside down in
heavy boots hooked to a bar) as therapy for lower back pain and
other muscular problems, but people with a number of medical
problems should be cautioned against this. Several cases of rupture
and bleeding of blood vessels in the eye have been reported;..." [
http://www.tagnet.org/abstracts/v2n4.htm ]. It goes on to list more
serious complications.

"What's more, dangling upside down can result in some unpleasant
side effects including headaches or bleeding into the retina." [
http://www.drweil.com/u/QA/QA38889/ ].

I also looked up 'petechiae' which Patricia mentioned: "Bleeding
that consists of pinpoint dots of blood is called petechiae." [
http://www.nlm.nih.gov/medlineplus/ency/article/003235.htm ].

I seem to remember reading somewhere that in the Gesta Danorum,
Ermenricus (=OIc. Jörmunrekkr) treats his prisoners in the same
way. As the Old English poem says of him, "þæt wæs grim cyning."