data1 = RandomVariate[NormalDistribution[], 1000];
data2 = RandomVariate[NormalDistribution[], 1000];
GraphicsRow[{
Rotate[Graphics[SmoothHistogram[data1,
PlotStyle -> Red,
Filling -> Axis,
PlotRange -> {{-3.5, 3.5}, Automatic}]], \[Pi]π/2],
Rotate[Graphics[SmoothHistogram[data2, PlotStyle -> Green,
Filling -> Axis, PlotRange -> {{-3.5, 3.5}, Automatic}]], -\[Pi]π/
2]},
Spacings -> {-234, 5}
]
(You may need to flip one distribution to keep the orientation of the vertical axes the same for the two plots.)