I'm sorry to hear about the experiences you've been having. It seems like there might not be specific information from the Huberman Lab available on this exact experience with the NSDR routine. However, experiencing unexpected effects during relaxation exercises like NSDR could be due to various factors, including stress or tension in certain muscle groups.
It's important to remember that not all techniques work the same for everyone, and sometimes, adjustments or different approaches might be necessary. If you're experiencing physical discomfort, it might be worth consulting with a healthcare professional who can provide personalized advice. Additionally, stress management techniques such as deep breathing, progressive muscle relaxation, or guided imagery could offer alternative ways to achieve relaxation and alleviate pressure.