What you are describing is a relatively common phenomenon known as "pareidolia" or "peripheral drift illusions." It is not necessarily a hallucination but rather a trick of perception that many people experience from time to time.
Pareidolia occurs when your brain tries to make sense of random or ambiguous visual stimuli, often leading it to interpret familiar patterns or objects where none actually exist. This is why you might see shapes, faces, or objects in clouds, patterns on walls, or even in the corner of your eye.
Peripheral drift illusions are a specific type of visual illusion where stationary patterns appear to move or shimmer when seen peripherally (in the corner of your eye), but when you look directly at them, they no longer appear to move.
These experiences are generally harmless and do not necessarily indicate any underlying medical or psychological condition. They can be more pronounced when you are fatigued, stressed, or in low-light conditions.
However, if you are concerned about these experiences or if they are accompanied by other unusual sensations, emotions, or disruptive effects on your daily life, it's essential to consult with a healthcare professional or a mental health provider. They can help determine if there is an underlying cause that requires further evaluation or if it's just a normal variation of perception.