The rule about emotional reactions in the field of psychology is consistent.
Whenever a reaction seems greater than would seem typical, emotions from another unmet needs are coming into the picture.
An example of this, such as you reference here, might be a man who is asked about his mother in a therapy session. Normally the reaction that most would have to this would not be emotional, but instead be conversational answers, and some minor expression of emotion, but not tearfulness and crying.
If this is the reaction the therapist could, in most cases, assume that the reaction is coming from feelings and needs that are unmet, unfinished and related to "mom".
Not knowing the client it is not possible to know exactly the reason for this reaction, but guilt, shame, past abuse and fear or betrayal, or combinations of them are common emotions that drive this sort of reaction. Certainly of this was my own client I would be asking a great many more questions about the relationship between mother and son as this reaction points to something significant. Steven