most antidepressants have warnings stating that they can increase the frequency and strength of suicidal thoughts while you're adapting to them, but I don't think that has to do with numbing of fear and emotions. In my personal experience this "numbness" would lead more to a lack of resolve to plan anything, but it might also make you functional, thus more capable to enact a plan, but I wouldn't attribute that to lack of fear. Different people have different experiences with medication though. If you're talking about a lessening of the survival instinct, I don't think antidepressants have any impact on that.