sachs shock rebound prob

[wence]

G'day ,
Today I road a great little track which had just about everything, sand, hardpack, creeks , very tight single trail etc etc .
I was playing around with the forks and shock and had it about right .
I just did a slight adjustment on the fork and shock and did a quick lap and a half when the bike went weird.
Rear shock started to act like a pogo, no rebound damping.
Played around when the lap was finished and could not get the rebound damping to work, even to the extreme of fully in(still pogoing).
Had a rest and a drink and got talking about suspension and a mate told me to ride his crf 450 with suspension done by a certain tuer who does a lot of pros gear.
Got back after a lap and went to get back on mine and it wa shard as a rock.
Adjusted it back and got it reasonable for the last half of the day but was just wondering what the deal was?
Anyone had a similar problem with a standard sachs shock?
Cheers Mark