I can't comment on 5-strings or technique as I don't have the former or enough of the latter. What I do have is some recent experience with wrist pain.
Long story short, I just returned from my 40th high school reunion where I played bass in a band with the same guys as back then. Great players. I'm no pro, so I spent a couple of months in the shed getting ready. I play an old P-bass with medium heavy LaBella flats.
A few weeks ago, I started feeling noticeable amounts of pain in both wrists and, like you, started to worry, not only about the gig but about longer term stress.
I tried regular stretching and pain medicine but the relief from those didn't last very long. What finally helped was adding ice to the therapy. Icing my wrists a few times a day, along with double doses of Naproxen (Aleve), made a huge difference. I had no problem playing 3+ hours at the reunion, and I still feel a tiny bit of discomfort, but it's a fraction of its former intensity.
Best wishes for your recovery.
Hozay