Answering your questions, along with some advice, please see if it makes sense to you:
1. In meditation the objective is to build a viewing platform/grounding object and simply objectify any and everything that arises which pulls us away fromm the grounding object. In the Mahasi technique the viewing platform is the rising and falling of the abdomen. We establish mindfulness of the rising and falling of the abdomen and when an 'object' arises that pulls the mind away from the grounding object - we track it till it subsides - acknowledging its existence using a mentally created verbal label. This labeling moves on to 'noting' - a mentally created and acknowledged pause - and that has to move on to simply being with / tracking the object simply acknowledging it and knowing it for what it is - this is called Yoniso Manasekara. The verbal label and the artificially created and acknowledged pause is supposed to help objectify the thing that has pulled attention to it. So when emotion arises - label emotion, note emotion, simply be with and track emotion till it disappears. Skill naturally increases from labeling to noting to yoniso manasekara. This is the core of the Mahasi technique. This for some people is problematic when emotional content arises which is too strong to be simply mindful of. Some degree of Shamatha or calm abiding practice done in parallel to the mahasi technique may help. What may also help is to learn a skill called 'softening into' taught in a system called MIDL .... relax mind and body when tracking object, track objects on the outbreath piggy backing on the relaxation of the diaghphragm and concomitant relaxation in the mind, track objects and physically sigh at them, track objects while dropping intentions of acting on them.
2. Every system of practice that involves establishing mindfulness in one of the four foundations of mindfulness will lead to phenomena arising of this nature. For different people this may happen with different severity at different points in their practice. In the quiscence of a meditation session a mosquito bite on the elbow may be accompanied with a tremendous amount of irritation setting off what is called prapancha or proliferation resulting in many irritable memories of the past also arising or scenarios of the future also arising. This is grist for the mill. When in meditation through the tracking of objects the mind starts to engage and track the gross and unique characteristics of objects and then starts to engage with the subtle and ubiquitous characteristics. Sound - sound - sound becomes loud - shrill - soft .. becomes start - middle - end becomes arising - dancing around - passing away. Same for every other object and every other sense door. This is the mind becoming sensitive to the mark of anitya - impermenance/unreliability. This naturally leads to the mind experience and tracking fear, misery, disgust, desperation to end. This territory is called the dukkha nana. It happens at a very high skill level and at that skill level the yogi knows what actually caused it. So there is dukkha but there is also the nana or knowledge of what it is and why it came about and how to let go of it. If this smartness is absent then it is only dukkha ... it is not dukkha nana. So if you are getting these wild emotions then to simply keep doing that which you are doing is a bad idea. Try and do shamatha practice in parallel, try and learn softening into and incorporate it into your noting practice.
Hope this helps.
