Following recent literature on dS instability in presence of interactions, we study the decay of massive particles in general FRW models and the emission from naked singularities either associated with 4D charged black holes or 2D shock waves, by means of the Hamilton-Jacobi tunneling method. It is shown that the two-dimensional semiclassical tunneling amplitude from a naked singularity computed in that way is the same as the one-loop result of quantum field theory.