It is interesting you mention this.
We recently climbed a technical 6000m peak in the Tajik Pamirs as a team of three. One of use got sick. My partner and I draged the sick and weak third person down through difficult terrain, fixing ropes for him, over 24 hrs on the go with the sick totally loosing it and the two of us going to our limits too to get us all out.
The next day I said to my buddy "you know, yesterday night it feel like we were four, not three. Feels like somebody else was there". He said then that this was very strange, since he felt the same way, that we were four, not three.
Never had that feeling before, but we both clearly had it that day&night.