Air carrier Captain reported a temporary loss of control during cruise due to severe turbulence.

Narrative

ZZZ Center had been talking about severe turbulence reports. We queried further as the FOM says not to fly into know areas of severe turbulence. He said they were all mountain wave. And changed our arrival away from the reports. ZZZ closed for windshear and we were given holding at ZZZZZ. The plane wanted to hold at 233kts. Because of the bumps and how close it was to the low speed queue I kept the plane at 260kts. At the initiation of the first inbound turn back to the hold fix. Turbulence increased from moderate to severe. Autopilot disconnected I assumed control. The plane had uncommanded roll in opposite direction from control inputs. I was just trying to keep the plane level and near target speed the flight instruments were difficult to see. We momentarily got a stick shaker I don't know how must speed was lost but it was significant and not appropriate in regard to where the thrust levers where. We reported the turbulence to ATC and requested to hold somewhere else. Everyone had been in their seats for several minutes prior to the event. We called the cabin when we had time no injures were reported to me besides the Aft flight attendants stated after the flight that they had 'muscle strains'.