The more accessible version of this, for me, is lying in the bath. The phone is out of reach and it's more effort than is worthwhile to get any props other than maybe a book I don't care about getting wet into reach. So there's just nothing.

In that situation I can usually last about 5 minutes before my brain says write that thought down, you'll forget it so forcefully that the bath gets cut short. Rampant unmedicated ADHD has a lot to answer for. So I can second the physical writing recommendation, if only because having a laptop in the bath is a really stupid idea.