Swamped

Your first thought is to check if he's left, whether by his own will or by force. Going through the front door is a sure way to get spotted - the tavern across the road is always full of gossips until it closes at dawn. You think back to the bomb you found, but the windows here are hard to open all the way. Slipping a clock inside is one thing - getting an entire person out would be difficult without making a lot of noise, one way or another. There's also a staff entrance at the back, but there's a locked door between it and the actual emergency ward. And the night doctor's the only one here tonight with a key.

That leaves the emergency exit. It's set to ring a bell if someone opens it, but the bell is easily accessible, so it would be easy to cut the string or otherwise disable it. Your understanding is that they couldn't afford anything more secure, and they figured if you had to be inside to break it, well, that was good enough security.

You make your way over to the exit, and examine the bell. Somebody's stuffed a big ball of cotton into it, preventing the clapper from moving. So they almost certainly used the door.

But this sabotage is also easily reversible. Take the cotton out before anyone has a chance to check, and your escape goes unnoticed. This suggests that whoever left plans on coming back.

So maybe Mortimer just wanted to stretch his legs. Or maybe whoever grabbed him is also a patient - there's an unusually large number of them right now, after all. It would be easy for someone to slip in with the crowd.

Of course, it might also have nothing to do with Mortimer and just be a coincidence. Except, you think you just spotted something which makes that seem significantly less likely.