Often people think that coaches are invincible/super human… but we aren't. You can do everything right: have a solid warmup, good technique etc but sometimes things happen!
Note that this is not medical advice - this is what I find works best for me.
Stop what you're doing
Don't be the hero and assume you can do another set. Trust me, it never goes well.
Book an appointment with your therapist of choice as soon as you can get in.
Everyone has someone, or some type of modality that works best for them.
But remember that these are always temporary solutions.
Assess your current movement abilities and the area of restriction with low level mobility drills.
The first thing that I usually do would be a joint range of motion assessment - something like a cat cow/spinal rotation to see what positions I'm restricted in.
Usually attempting to foam roll or release the area does not work when it's too acute and flared up.
I find the most beneficial thing to do is to actually walk. Make sure that you walk with a good arm swing to allow rotation through the spine.
I will also do some positional breathing drills to drive expansion to the compressed areas.
Try to stay active -When you stop moving is generally when it starts to get worse.
Once it's less acute and/or you've gotten in to see a therapist, I will do some mobility and movement work.
I will gradually progress the intensity and start to add exercises that don't cause pain, increasing the load over time.
Note this may take 1-2+ days or weeks depending on your situation
Be patient and keep moving. There is always something that you can do in the gym. I'm also a big fan of heat: hot baths, hot tub, sauna..
Do what works for you - and hopefully some of these pointers will help you!