Bummed that you might have to stop riding, Catrin, but I understand your dilemma. And I agree that carrying a recumbent or trike up stairs would do your neck and shoulders no favors. The only possible option would be a much lighter-weight short-wheelbase (SWB) recumbents. I believe they weigh in the same range as upright bikes, so if you're able to carry your Gunnar up and down, that could be an option. Have known several folks with various back or neck issues (including a good buddy who has chronic neck pain) who have found relief on a 'bent. But as others have pointed out, they could actually aggravate certain issues, so it's just very hard to say.
I surely wish you the best, no matter what! And am still very grateful for your Jamis -- it's been a wonderful bike for me over the past almost-year now!
Emily
2011 Jamis Dakar XC "Toto" - Selle Italia Ldy Gel Flow
2007 Trek Pilot 5.0 WSD "Gloria" - Selle Italia Diva Gel Flow
2004 Bike Friday Petite Pocket Crusoe - Selle Italia Diva Gel Flow