Funny how this works - this time round, I might actually have a "wise word" or three for you. :)
Let me start with a disclaimer, though: I am no longer doing this job. Went for a radical change two years ago, but that wasn't anyone's "fault" but my own. The support I got from the bosses once sheer necessity (spell it out NOW or run screaming and end up unemployed) made me ask for it was nothing short of amazing, even in a field not commonly associated with compassion.
I'd been off sick on and off again, just trying to wrangle a life that'd been flipped on its head in every aspect that mattered (and failing) for a year, getting more stressed out and paranoid about the job-situation with every passing day thinking "surely they're not going to watch this much longer, I'm doing nothing but costing them money and freaking out", yadayada. The kind of thought that certainly doesn't help when you're trying to regain at least part of your footing.
Full-on "waste of space" frame of mind.
Like your employers, they were incredibly patient with me, though, and - having witnessed/heard of the ways things like these get handled at other companies - I've come to see that as a mighty good sign.
Back then, though, I pretty much "blamed" the fact that they couldn't fire me while I was "sick". Surely they simply were waiting for their chance to do it next time I came back, blah, blah, blah.
Well, they weren't. I returned to work once again and the head-honcho called me into his office on my second day back.
I was a MESS, hid in the bathroom for almost two hours before, still don't know how I even managed to walk in there more or less on time. I was convinced this was it, I was outta there, unemployed (and probably unemployable forever), doomed to starve in the streets. It felt like walking into the Apocalypse.
He asked me to sit, I couldn't, and before he had even taken a breath to start speaking, sheer panic overrode misguided pride somewhere in my brain and I blurted it all out to him.
I apologized over and over for not being the employee they needed me to be, thanked him for being so patient, attempted to explain (leaving out the four dreaded letters I was still refusing to see were attached to me) and finished by basically telling him I'd show myself to the door.
I hadn't even turned around yet when he said the one thing I never would've expected anyone to say, especially not in this line of work.
Still hear it today.
"What do you need us to do so you'll stay?"
To be honest, I don't remember what exactly I told him then. I DO remember being a mess through it all, and I most definitely remember the steps the bosses took after to provide a healthy environment for me. They pretty much rewrote my entire job-description, took me off the tasks I'd actually been hired for, made sure I didn't have to deal with too many people, moved my desk so I could work with my back to the wall and a clear view of the room and all doors etc.
They even adjusted my hours so they'd work with my therapy and those days where I'd need hours to recover from the nightmares. Basically...they did everything I could've wished for and more, simply because they valued me as an employee and finally knew (more or less) what the problem was.
Now - I'm not suggesting you should walk into your boss' office and lose your dignity like I did, but I don't think that's where you're headed anyway.
You're thinking this through beforehand and you're preparing for it, so that risk is low anyway. :)
What I'm trying to say is...if they didn't value your contributions to the company, they wouldn't be this patient. They truly seem to want you there, and that's a pretty solid foundation to build on.
If you have options as to whom to speak to about this, choose the person you feel most comfortable with and just go from there.
Try to make sure you both have enough time for this talk (best you can), and start with what they already know about the reasons you were gone, then go from there without leaving yourself too exposed.
Depending on the person you're talking to, you might have to spell out your needs like they are about 5 years old, but I believe you're well aware what kind of support you'd need from them and what you've got to offer in return, given a healthy environment, so I guess getting that across won't be a problem. It's all absolutely terrifying, but so, SO worth it in the end.
Sure, there's no guarantee that they'll be willing/able to work with you there, but I'll say it again: Their patience is a good sign, and stuff like that CAN work out, I'm living proof. :)
In the end, it was my own inability to NOT get involved when others came to me with questions regarding what'd once been my part of the job. I ended up taking on most of my old duties on top of the new stuff and finally had to admit to myself that this was not something I'd be able to stop myself from doing any time soon, so I had to make the decision to walk.
To this day, I'm in touch with my former employers and they've let me know that the door's always open for me, should I decide to return.
I don't think I will, but I definitely always will remember what they did for me, and that all I had to do for that was ask.
Best of luck to you, if little old out-of-control me could do it, you most definitely can. :)