We consider vacuum transitions by bubble nucleation among vacua with different values and signs of the cosmological constant Lambda, including both up and down tunnelings. Following the Hamiltonian formalism in four dimensions, we explicitly compute the decay rates for all possible combinations of initial and final values of Lambda and find that up-tunneling may be allowed starting not only from pure dS spacetime but also from pure AdS and Minkowski spacetimes. We trace the difference with the Euclidean approach, for which these transitions are found not to be allowed, to the difference of assigning either vanishing or infinite entropy to both pure AdS and Minkowski. We find that, in all allowed cases, detailed balance is satisfied. Also in the formal limit Lambda -> -infinity, the transition rates for AdS to dS agree with the Hartle-Hawking and Vilenkin amplitudes for the creation of dS from nothing. This is consistent with a proposal of Brown and Dahlen to define 'nothing' as AdS in this limit. We generalise our results to include black hole backgrounds for which transitions are allowed only in certain regimes of the black hole mass M but detailed balance is not satisfied, except for Schwarzschild de Sitter (SdS) to another SdS for which the transition is allowed and detailed balance satisfied. We compute the bubble trajectory after nucleation and find that, contrary to the M = 0 case, the trajectory is not a geodesic for the open universe slicing of dS. We briefly discuss the relevance of our results to the string landscape.