As one of the positive social interactions, being in love activates brain structures that trigger myelinated vagus stimulation. The myelinated vagus then activates the parasympathetic nervous system, reducing your stress levels. When stress and fear get out of your way, a sense of body relaxation and comfort automatically takes over. The result? You are more likely to feel sleepy.
If You Feel Sleepy Around a Person, Is That a Sign of Love?
Feeling sleepy around a person(co-regulation) means you have a strong relationship with them. So yes, it can be a sign of love. It is worth noting that the co-regulation is not a thing for familial and romantic relationships alone. Other relationships can experience this effect, only that its intensity is much lower compared to the aforementioned relationships.