I had a liver biopsy years ago. I can remember being worried and a bit scared, but the biopsy itself was fine and over very quickly, the staff were very reassuring and capable. The tough bit was having to go on a ward and lie absolutely still for several hours (presumably to reduce the risk of bleeding), I found it physically very hard and got very stiff and achy...but nothing that didn't wear off once I got moving again. Sorry I can't help much. I hope your DM recovers quickly.
From what I remember it was a bit like being punched, or having an epidural put in. All the stuff about being really still, and knowing that it is all happening, so it is scary but not really painful IYSWIM.