Regarding negative feelings after meditation, I am grateful that you mentioned it because I had these too and this is the first time I've heard from anyone with a similar experience.
I took up regular meditation last Spring, sitting 30-40 minutes daily in my best approximation of zazen. I found the meditation quite relaxing and on some days I felt much better afterwards or had small insights about my life. Other days were not so pleasant. I believe I experienced a sharper awareness of the stress I felt at work (which in the past I would have denied feeling at all) and I was much more likely to notice when I became distracted at work, resulting in growing frustration and anxiety. I think it also made me more aware of the shallowness of my relationships with my coworkers and my own reluctance to engage with them.
Overall I suppose it's been a positive and educational experience.
Preparing you for these (transient) negative feelings is a standard of Buddhist meditation teaching. At least it's in the foundational texts and it was mentioned in the few Buddhist groups I've attended. It would be unfortunate if modern meditation guides would leave that out.
I took up regular meditation last Spring, sitting 30-40 minutes daily in my best approximation of zazen. I found the meditation quite relaxing and on some days I felt much better afterwards or had small insights about my life. Other days were not so pleasant. I believe I experienced a sharper awareness of the stress I felt at work (which in the past I would have denied feeling at all) and I was much more likely to notice when I became distracted at work, resulting in growing frustration and anxiety. I think it also made me more aware of the shallowness of my relationships with my coworkers and my own reluctance to engage with them.
Overall I suppose it's been a positive and educational experience.