A fun exercise is to calculate how much mass in rocket fuel you would need to accelerate at 25G for two weeks. Or even to accelerate at 1G for a year. Even if you assume a ridiculously high ISP like 1 million seconds (our current best engines are around 8,000 ISP, and they're severely limited in thrust) and close to unlimited energy to add to the mass. Like you're using antimatter to kick propellant out the back at relativistic velocities.

Now add in the mass to slow down once you begin to approach your destination.

I know I am not taking relativity into account but outside of that it's something like 250 kilograms (~550lbs) of antimatter (and that value again for the matter for it to react to) or the equivalent in other fuels. The only difference is how quickly you burn through it.

Which doesn't sound like a lot but its probably as much or more antimatter than exists in the entire solar system, so if it were the fuel then whoever was using it would need to have figured out a method to create and store antimatter in bulk along with the ability to react antimatter as rocket fuel without destroying the rocket its fueling.