The Collaborative International Dictionary of English v.0.48:

decompressing \decompressing\ n.
   1. the process of experiencing decompression; the act or
      process of relieving or reducing pressure.

   Syn: decompression.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

decompressing
    n 1: relieving pressure (especially bringing a compressed person
         gradually back to atmospheric pressure) [syn:
         decompression, decompressing] [ant: compressing,
         compression]