First you need to re-establish sensitivity. If your receptors are indeed desensitized/downregulated pretty much any intense training program will, at best, keep things the same and at worse, increase the desensitization.
If you’ve read some of my articles you know that 5 main things can increase cortisol production in the gym:
Volume: cortisol plays a big role in energy mobilization. More volume = more energy needs = more cortisol to mobilize it
Intensiveness: how hard you push each set. The closer you do to failure (or even beyond) the more cortisol and adrenaline you produce
Psychological stress: This is often related to using big weights that somewhat intimidate you, but it could also be doing energy systems work to the going to not being able to breath properly
Neurological demands: the more demanding on the nervous system the program is, the greater is the need for CNS activation which means greater adrenaline production. More complex lifts, more explosive work, heavier weights, Alternating exercises (e.g. A1/A2) or adding new complex movements are all elements that increase neurological demands.
High training density: The shorter the rest intervals are, the more adrenaline you produce (and thus also cortisol).
If your situation you will need to lower 3-4 of these variables for a good 7-14 days. YES this essentially means doing a training program that will not trigger progress, it will help you maintain though.
You need a low volume (1 work set per exercise, 2 warm-ups, 4 exercises per session), low intensiveness (stop 2, even 3 reps short of failure), low neurological demands (switch to mostly machines for 1-2 weeks, do not alternate exercises) and even increase the rest intervals to 3-4 minutes between sets.
As for frequency I would recommend 3 days a week.
Again this is only for 1-2 weeks. Honestly it’s either that or take a week off completely.
It’s not like you are making gains right now anyway.
As for nutrition, make sure that during those 1-2 weeks, you are in a caloric surplus and eat carbs at every meal (it will help decrease cortisol and adrenaline). Don’t worry abut gaining 1-2 lbs of fat, you will easily lose that later: the goal is to get your CNS back in top form ASAP.
As far as supplements are concerned I would recommend SAM-E (around 1000mg per day). This will help with mental state and with adrenaline clearance.
If you don’t mind have zero energy for a week, the best blitz approach you can use for your problem is taking 1mg of melatonin every hour starting at 10am. If you feel too fatigued you can go 1mg every 2 hours starting at 10am. Metalonin will essentially kill cortisol production. YOU ONLY DO THAT FOR A WEEK. And will help you re-establish a normal cortisol cycle.
On week two switch to taking 1mg every hour after 5pm, and you do that for a week.
By almost completely killing cortisol and adrenaline this will rapidly re-increase sensitivity.
As for after your 1-2 week(s) “deload” I recommend doing a program where you only focus on pushing one variable very high. Do not mix high intensiveness (going to failure or 1 rep in reserve) with high volume. I personally prefer to push intensiveness and keep volume low for the natural lifter. My “Best Damn” programs, but done for 4 days a week at first would be the best option.