In this paper, we investigate F -hypercyclicity of linear, not necessarily continuous, operators on Fréchet spaces. The notion of lower (mn)hypercyclicity seems to be new and not considered elsewhere even for linear continuous operators acting on Fréchet spaces. We pay special attention to the study of q-frequent hypercyclicity, where q ≥ 1 is an arbitrary real number. We present several new concepts and results for lower and upper densities in a separate section, providing also a great number of illustrative examples and open problems.2010 Mathematics Subject Classification. 47A16, 47B37, 47D06.