let me think about this... From a layman's understanding of gravity, it's generated by a planetary body and is bubbled around the planetary body. Anything coming into contact with it will be attracted to that pull of the planetary body's gravity well and be drawn down to the pull of the well (Kersplat!). So far, so good, if you have enough momentum greater than the pull, then the pull doesn't affect you (may deflect your course abit) but you negate its effects ( the whole plus/minus thing).
Zero - g (ie: in space not near to a planetary body) you wouldn't be affected by the engine thrust as it is outside in a non gravity environment, and any maneuvering wouldn't necessarily affect you so you could actually move about on a ship as it was doing somersaults and tripping the light fantastic as the thrust is relative as you are moving at the same speed. Unless you hit part of a gravity well (Star, Planet,Moon, large asteroid....) then it would depend on the strength of the gravity, how close the ship is to the gravity and to the speed the ship is travelling to determine if it is greater than the gravity pull ... everything on the ship (including the pilot) will be travelling at the same speed. So the danger points would be exiting Frameshift drive and appearing ontop of the system star, landing on or taking off from a planetary body... but in 3300AD I would assume the computer astro-navigation tech would be at a level as to know how to manage these situations so as to not cause squishy human blancmange!
Therefore yes you would be advisable to be seated and belted in place for when you pull away initially (take off - think of modern jet airplane and the feeling of the thrust of the engines), but you wouldn't have (and I guess the engines wouldn't allow for...) escape velocity 0 to whatever mph immediately the ship needs, according to the planetary body. You would probably be flying much less than Mach 1, in the beginning until ship systems unlock to allow for orbital flight and supercruise acceleration... Additionally, wouldn't you be travelling away from the ground at an angle initially rather than straight up. The gravity lessens as you rise higher and higher away from the ground; meaning more thrust isn't as oppressive as the gravity lessens, especially high altitude ascent- low orbital flight as it would be initially... as long as you are tanked up with oxygen in the ship to stop hypoxemia... then I don't see the problem.
I think I've got that right!