Sorry, not a clue........unless there is some grit, etc. hanging around the trigger mechanism. If the trigger is messed up, you can buy a new one for $25 bucks or less (I would recommend a 3.5 lb., it's not really like a 3.5 lb. on a single action). If it's yours, remove the slide and spray it good with brake cleaner to blast anything out of there then oil it real good.
Could have been a severe lack of lubrication, too. I've handled a few that felt like that after being blasted out with brake cleaner/gun scrubber, and then not lubricated (or lubed properly). If you completely degrease ANY gun with a spray solvent product, it can do weird things to the action's feel/function.
(Not picking on Charlie's above advice, as a LOT of folks use that stuff; just reporting what I have seen.)
DJ Niner is correct about any gun not being lubed. In retrospect, I would advise the gun be generously lubed BEFORE being de-greased to see if that solves the problem. If not, then get in there an clean it good with Hoppes, de-greaser or whatever, but just be sure it is lubed when you try it again. And again, if you completely de-grease a gun, you MUST completely lube it before working the action.
I've owned Glocks since 1993 - My Glock trigger feels like any other Glock. Didn't know if you had been exposed to that brand before. As I get close to the breaking point, the Glock trigger gets a little spongy - not sure how else to describe it.
My night stand gun was my Glock 34 - but I've been shooting my P99s so much, that I know that trigger by heart. I don't shoot the G34 much. Last time I did, I was way outta practice w/ the trigger. So, I bought an M5 light, and my SW99 is my new night stand gun now. I figure that if I wake up in the middle of the night and need it, I want something that I am super familiar with by instinct...