I’m totally unqualified to give any advise but that doesn’t stop me sharing my experience - Sorry.
Recently I thought I was going backward. Cord changes getting less accurate and slower. Feeling more of a gumby than normal.
Then it struck me. I had been progressing pretty well and feeling more relaxed so I was practicing on the bed and the low comfy couch - Mistake!
I realised what I was doing and went back to an upright position on a firm chair with the guitar held as Justin instructed in the first lesson. Voila! back on track.
Thanks for sharing your experience! You’ll help a lot of people who might not be aware of their posture, and how incorrect positioning can hinder progress.
I’ll share something too… I’m an intermediate player who has always struggled with posture, and it’s been holding me back from progressing. Determined to finally solve the issue, I started practicing in front of a full length mirror… so I could see what the problem was.
After struggling for 2 years, it took all of 10 minutes to realise what I needed was a strap that wouldn’t slip! Replaced it with a rawhide suede backed strap, and suddenly it wasn’t so easy to pull the guitar out of position. Problem solved! Sharing your experience might just help someone! Cheers!