Well now that you mention it..
It was a solotrip on truffles at night, I was already in bed.
For the most of the trip I had my eyes closed, but sometimes I was just looking around having a good time, thinking about and enjoying the visuals that are so much more clear and present in darkness. So I was watching the curtain wave and my eye fell on this dark corner where a structure on the celing meets the wall.
There was a black thing going on, and it started growing along the lines of the structure on the ceiling. No body or so, just some black erratic form that grew on me. I could not see depth in it. At one point I realised I could not see if it was at the ceiling or straight into my face. I could not tell if I was really seeing it with my eyes, or as a projection of some sort. The main part of this form was streched out from the corner all the way across the ceiling to my left side. And eventualy the whole left side of my vision was occupied by this form. I remember quite clearly because I was really studying it. When I really focused it was not black at all. The black was just the outline, like a background. On the foreground there were lines moving along the length of the black form. These lines were like frequenties going mad. Some high amplitude, some not, some high frequency, some not. There was green, purple, yellow and also I remember small orange dots bouncing around. The lines were moving very fast, like sparks of electricity, and it was difficult to take a good look at them. The outline of the black form was also moving fast, it looked spiky. It was abstract, did not look organic at all.
At one point later I went to the kitchen. When I returned and looked at the curtains then the form appeared again and grew again from the same corner at the ceiling. Been looking at it twice for quite some time. But I never figured this to be an entity. To me it was more like a growing 'form', visual, or maybe some code because of the erratic frequency like thingy happening.
Anyway, next trips I will be searching for this form.
Maybe it was always there?