That nirvanic experience can be quite powerful. Your reaction to it could have very likely been your own undoing. When the feelings became overwhelming, your resistance as opposed to unconditional surrender ensnared you. You probably weren't ready for this experience. You probably could have used some more practice in surrendering and letting go at lower levels to prepare you for such an intense experience. When I had my first nirvanic experience, it was indeed quite intense and was one of the first times I found myself thinking, this is getting to be a bit much, but because I didn't resist and I just surrendered to the infinite power before me, everything went so smoothly and euphorically. Resistance leads to trauma.

Perhaps, but I think when that happens One will just split into a new multiplicity after a while.

Unity may be enjoyable sure, but it's not very diverse. IMO, the purpose to living is to amass a variety of experiences not attainable in the unitive state.

I think that is the trap to be fallen for: that things have to be one way or another. That anything must exist in either one state or another. I think it's a matter of perspective and processing. Take for example the triangle. The triangle can be perceived analytically as 3 distinct lines, or it can be perceived holistically as a triangle. In a similar manner we can choose to perceive the universe as One big whole. It is One. It is the entirety of everything that composes it. We can also see the universe (and thus ourselves) as distinct and separate components from everything. As the left brain (analytical) dominant as humans tend to be, we tend to see ourselves as distinct, but it's really not an "either or" situation, it's a "both and" situation. We are both distinct components of the universe at the same time as we are One with the universe. These ideas are not contradictory. What appears to be a paradox is merely improper processing.