Does deceleration (or negative acceleration) feel like acceleration? This may seem like a dumb question, but I'm having a hard time trying to intuit the answer. The question is in relation to Einstein's famous thought experiment which says that it is impossible for a person to determine whether she is at rest or moving at a constant velocity.
To build on that, let's consider the following thought experiment: suppose a person is sleeping in a train carriage, and when she wakes up she cannot tell if the train is moving or at rest, or in which direction the train is moving. Now suppose the train is in fact moving on the tracks and then decelerates until it comes to a full stop. If the person cannot look outside, and has to rely on pure sensation of motion (disregarding sound of brakes or anything of that sort), would the person on the train be able to tell the difference between the train moving and then coming to a stop, and the train being at rest and then accelerating? In other words, does deceleration (or negative acceleration) feel exactly like acceleration?
 A: Deceleration is a "special case" of acceleration. More precisely, acceleration is given by the vector $\vec a$ which has both a magnitude and a direction. Sometimes the same vector $\vec a$ increases the velocity $\vec v$ – when they are oriented in "mostly the same direction" – and we speak about "real acceleration" in the sense of an increasing speed. And sometimes it decreases the magnitude of the velocity $\vec v$ – when they are oriented in "mostly the opposite direction" – and we speak about a decelerating speed.
A person only feels the acceleration vector $\vec a$. He doesn't feel $\vec v$ and he doesn't feel anything about the relative properties of $\vec v$ and $\vec a$. A person in the train can distinguish whether the acceleration vector $\vec a$ is pointing in the "front" direction or the "backward" direction. But he can't know in which direction the train is going. He can't feel $\vec v$.
Consequently, the passenger sitting and looking in the direction of motion – like the driver – in a train that is accelerating has exactly the same feelings as a passenger sitting in the opposite direction in a train that is decelerating, and vice versa.
When gravity is included, the more correct statement is that the passenger only feels the direction of the total gravity-like acceleration field $\vec g - \vec a$ in the convention in which $\vec g$ points towards the center of the Earth (down). The sign in front of $\vec a$ is the opposite one because if one accelerates to the front, it feels like gravity dragging us back. Both the magnitude and the direction of the vector $\vec g - \vec a$ may be felt. Unless the train's acceleration is huge, the magnitude will be basically close to that of $\vec g$ i.e. $g$.
However, the direction of $\vec g - \vec a$ may be felt as well. This direction is not vertical if $\vec a$ is nonzero (and not vertical). So what the passenger feels in the accelerating train is "tilted gravity" pointed in a different direction. In particular, a train that is accelerating while going down the hill (and similarly a decelerating train going up) may feel "exactly the same" as a non-accelerating train on horizontal tracks if the angle of the tracks and the ratio $a/g$ obey a certain equation.
A: Imagine a space ship ran put of fuel and a second is going to help. They will do a  docking maneuver to hand out some fuel.
Now, the second ship has to adjust its speed when it's near the first (because the first can't change its speed).
A passenger on the second ship feels the acceleration. But does the ship accelerate or decelerate? 
If the first ship is at rest, the second is moving and has to brake.
If the second ship is at rest and the first drifts towards it, the second has to accelerate.
But in space, it's impossible to define an absolutely not moving point, and you can not say whether the first or the second ship is at rest. 
So, both cases are exactly the same, and there is no physical way to distinguish acceleration from deceleration.
And because there is no physical difference, humans can't feel it, too. 
They can't feel speed, and now just feel a force (including its direction). But they can't say if it accelerates or decelerates them.

In reality, you choose large objects like the earth as reference system and interstellar ships may use stars (though that's all not absolute nor perfect) to define what is at rest.
You know this weird feeling of "are they moving or are we" when sitting in a train in a station? The acceleration is very low for the first moment, so you would not feel it. The other train is large and the station (reference) is out of sight. Without that reference, you're lost, until you see the station or start to feel/miss the increasing acceleration.
By the way: A lift is a much better example for your question, because it moves smoother, acceleration and deceleration are almost the same, and it hides the reference system (except showing floor numbers on the display). 10 seconds after the doors closed, you feel you are getting heavier. Did you miss the getting-lighter feeling when the lift accelerated downwards? Or was it not yet moving and is now accelerating upwards? You don't know.
