If you place cannabis seeds in a glass of water to germinate, sometimes they float, sometimes they don’t! So don’t worry if they do sink, they will not drown.
However ungerminated seeds run the risk of developing rot in the taproot, which is why after 36 hours you should remove them. For this same reason, with the tissue paper method it is important that the paper is moist and not submerged under water.
Always follow the Goldilocks rule – Not too wet, not too dry, just moist!