Taken from news.com

Deep vein thrombosis has been associated with long-haul
air travel, but people who work or play for excessive periods
at their PCs are also at risk of developing blood clots that
could lead to DVT, according to a new report.

Research published in The European Respiratory Journal
reports that a young man in New Zealand nearly died
after developing DVT following extended periods of PC use.

This first recorded case of "e-thrombosis" occurred after the
New Zealand man spent up to 18 hours a day using a
computer. He developed a large blood clot that formed in his
leg veins, then broke off and moved to his lungs...

Read the full article here

Time for lower the time spent on the comp .