Every real-world object that you see around has a 3rd dimension and that is the reason why you can take it and rotate it to watch it from different angles. The sketch you have drawn had a length and a width, since the paper you used to draw also had a length and a width.
But there's no thickness (3rd dimension) so your sketch doesn't have that extra dimension either. There are many companies available that provide 2D and 3D animation services. You can easily get the best 2d and 3d animation services via https://dezpad.com/service/3d-2d-animation.
For example, you don't sketch your imagination on a piece of paper, but you decide to sculpt it on a handful of clay. Since the medium (clay) you are using has volume, you must determine the shape of the cat from all angles when modeling.
Image Source: Google
Therefore, subconsciously you have added this 3rd dimension and therefore you have the freedom to rotate it as you wish.
Before computers played an indispensable role in the animation industry, everything was done by hand by animators, who were basically artists. You will create a series of slides with images on them, with each slide image a continuation of the previous one in order.
For example, when an animator wants to simulate a falling ball, they create a series of slides with the first slide representing the ball on top.
The next slide shows a ball, it can be 1 cm lower than the first slide. Below next again and so on until the last slide shows how the ball hits the ground. When the viewer is shown the entire sequence of slides at a rapid pace, the feeling appears as if a ball is falling.