Wetness and stains on sofa went away without washing

Asalamalikum,Hadhrat Mufti Sahab, about a year ago I had wet dream in morning while lying on a sofa. Waking up I saw the stains but didn’t know the concept of najasat that it transfer too – I didn’t wash it and after some time it dried and then after some time stains were also gone. So my question is:
Does the clothes and Musallah get napak and we can’t go to mosque with those clothes because we sat on it? my mind is very disturbed by this. Please help, JazakaAllah