Hello again Srdjan,
It is very hard to diagnose people through a forum post, unfortunately. The first thing I want to say is that what you got seems nice and valuable. However, this is not what you asked... so, some things you said make me doubtful that it might have been a cessation:
1) You mention "black nothingness", but in cessation there is no colour to speak of (and black is, of course, a colour), and there is no nothingness that can be perceived (and nothingness can, in fact, be perceived, for example in 7th jhana). In fact, there is no perceiver, no perception, no nothing at all.
2) The fact that your body jerked during the blackness makes it sound very unlike a cessation.
Common candidates for things to be confused with Cessation include the A&P, Dissolution, the 7th jhana, and all sorts of near misses and state shifts. Your description of emotional side effects makes me think it might have been something A&P-like. In fact, when someone comes on this forum thinking that they got cessation, 9 times out of 10 it turns out that it is was actually the A&P, or something else.
This doesn't mean that you are practicing wrong, or that the benefits that you mention are not real or valuable or to be disregarded. In fact, I would suggest to keep doing whatever it is that you are doing, as it seems to be doing something good for you.
Hope this helps, perhaps more people will chime in.
neko