I had that happen to me not long ago. Totally frustrating. What I found that helps me, is to just hit the ball... no thought swings at all. All those good swings are in there you just have to find them... I also think I was standing to close to the ball, half a step back really helped me out.
Now if it would only stop raining...

If all else fails, a large gin & tonic and watch the evening news - Usually seems to put things back into perspective.

I hit the practicece green and work through a bunch of balls, nothing like hearing the ball hit the bottom of the cup. Does wonders for you.

beer, sleep, repeat

If it happens, it happens. It's golf.
If it happens 2 or 3 times in a row seek advise. Maybe a buddy who knows your swing. Also focus on the landing area, your mind will make the swing to get you there.
Don't think of the swing just the target.

What you do (or don't do) on the range really shouldn't matter (too much) out on the course. Many extraneous factors are in play during a typical round that make you think so many more thoughts as opposed to just pulling the next ball out of the bucket and slapping away. I like your idea of playing an easier course just to get back in the rhythm and flow.

I’ve been struggling with tempo for what seems like months but actually only a week. When it gets bad, I go back to half swings & slowing way down. Get the alignment sticks out & think about anything other than tempo. I hyper focus on something else and let the “feeling” come back. That’s me anyway, I’m not smart enough to think about it.

sometimes I would just take a break for a day and try again tomorrow!

Try to end with one good swing and result, then quit.Resist the urge to hit another one.Couple of pints, lots of sleep and see what tomorrow brings.

I usually follow up a poor range session by careering my next round on the course. It's a funny game like that.

In all seriousness though, I think there's a lot of good advice in this thread. The more I play and the better I get, the more I laugh off poor shots, rounds, and range sessions. I really like the idea of ending on a good one though so I'm going to try and adopt that to avoid any post driving range blues.

If it's going bad you tend to try harder which tends to multiple things and make it worse.

Back off and stay loose! Easy swing don't try and hit the ball at all.

Read the responses their all good. But consider this. Get your driver out and do this. Tee it up as you usually do and have this one thought; try to hit your driver 150 yards! What? This will slow your swing down and have you swing under control. Make sure you finish your swing. Do this about 10-15 swings and then grab your 7 iron and just swing away. Swing the driver extends your arms and makes you swing with a full shoulder turn.

I just chalk it up as an off day. Ive learned not to go to the range if Ive had a bad day or have something on my mind because its guaranteed to be shank city.

Go to the clubhouse, grab a Burger and a cold beverage and kick back for a while. Then head home. Tomorrow's another day.

I try to go back to the basics.

Grip-Stance-Posture-Alignment-Ball position

Usually I have deviated off the norm when things go wrong.

I have kept a moleskine notebook in my bag for quite a few years with notes on the feels I have when I am hitting it good and what happens when they go wrong. Over the years, I usually do the same things wrong and what I have done to fix myself. (Probably more important when you hit it good to determine why then when you hit it bad)

I try to start there when things go wrong and last but not least, video your swing and try to work it out.

Beyond this, go see a PGA professional.

Good luck