First of all calm down, you're not going to lose your job!
Deep breaths, you won't find it in 'panic mode'.
It's easy enough to get locks opened & keys replaced, it's a bit of a hassle because everyone's laptop is in there, but it's most certainly not the end of the world!
It's most likely to be somewhere daft like on the kitchen side where you took your dirty much or the fridge where you put the milk back.
How far away is work, can you enter the building at this time of night?
If it's not too far & you can get in I'd go back, think about other things you might have done in your rush to get DS. Scooped pens etc into a drawer, cup etc into the kitchen, popped to the loo... it's almost certainly somewhere safe that you've just inadvertently 'put it down'.
Stop stressing yourself out, it's just a bloody key that can be replaced!!
FAR more importantly, how is DS?