What Flying Stone said.
If you have deliberately entered the spin in suitable conditions, you will know which direction it is going. If you have accidentally entered a spin with the horizon in sight, you will know which way it is going.
If you have entered a spin with inadequate visual reference to identify the direction, you should not have been flying that way there, in the first place, without adequate instrument flying training. That training will teach you to recognize and recover from unusual attitudes.
In a spin approved aircraft, with the right amount of space around, and under you, a spin is a very safe and worthwhile maneuver to practice for improving pilot skill. The rotation may seem a little fast and blurry the first few times, but as you do a few, they will seem to slow down, and you'll have a sense of more time to observe, enjoy then recover.
First, we do not have a skill. Then we gain that skill, but not yet the familiarity to completely demonstrate it in "real time". With practice, the skill improves, but more so, our ability to always "be ahead" if it improves.
Go an take aerobatic training, and do spins. The more you do it, the less blurry the rotating world will seem!