Can't have been the Cursed Halberd because I had already found it and stashed it away for future scrutiny. The loss of stamina started while in the House but continued after I left it. Then, I noticed that stamina was restored by successfully killing opponents. Unfortunately, I got into a major skirmish and was killed without having a chance to check my inventory to find out what strange item I had picked up. Loaded a saved game and the whole incident was just a memory. Oh, well ....
