I had a 4-level (L3 through S1) a bit over 2 years ago. Pic attached. Ten days in the hospital; a week or two resting. Then rehab...about 6 weeks @ 2x/week. Most people go a lot longer and don't recover as quickly but I've always been a rehab freak and bounce back very quickly. Bike time, leg presses, etc. The whole point is to strengthen the muscles that support the back, especially the erectors. However, things like the quadratus lumborum (QL) and glutes are very important too.
The biggest thing is that you will be wearing your brace for a lot of months...three or four at least. One thing you won't be able to do is touch your toes again...LOL... Depending on the location, cervical, thoracic or lumbar, the recovery can be very different with various restrictions depending on location.
Pain... You should be on major opioids (hydrocodone or oxycodone) at the beginning. Note: Hydrocodone causes constipation in many, many patients. Go with the oxy instead. Ask for Percocet. Exact same painkilling relief (NIH says so); different base molecule. You should be on them for less than 30 days and then switch to Tramadol or 800mg Ibuprophen. Get off the heavy stuff as soon as possible. You can't be taking that crap and driving to PT. Big no-no. Addiction in that short a time frame is a non-issue.
PT... Gotta take it VERY seriously. And you're not done when PT time is over. This is a year-long recovery that will be all on your shoulders. Gotta hit the gym. Example: Golfers who have a fusion are warned not to even swing a club FOR SIX MONTHS and then re-engage slowly and gradually over the next six. Remember...FUSION means that the bones have to FUSE together. This takes time...you cannot mess with it and just return to "normal life". There will probably be lots of restrictions on bending over...you have to learn how to SQUAT to pick things up. Plus NO TWISTING!!!. To get out of a car, turn with your back straight and move BOTH legs to the ground...then stand up. Torquing your back is a major no-no...especially during year one.
I still wear my brace to do housework and gardening...it keeps me from even thinking about bending over. And no slouching in a chair!!! Get an ergonomic one that maintains good posture.
That should get you started. Yeah...it's some pain at the beginning. Manage it properly. I wrote this for my TKR group but it still applies...
https://patient.info/forums/discuss/staying-ahead-of-the-pain-563395
Hope this helps.
PS: It's not as "intense" as you might assume. You go to sleep, wake up, take your meds, go home, wear your brace, do rehab. Easy. Don't set this up in your head as something completely awful. You'll handle it just fine. Just avoid the Jedi Mind Tricks...
PPS: Just had a LATERAL one-level fusion (LLIF) above my old one about two months ago. Pic attached; they go in from your SIDE not your back. Overnight stay...zero rehab. That was sooooo easy and all the stenosis pain was gone instantly!!!