Ever see those silly YouTube videos where a baby is both scared and delighted at the same time. Go ahead and give it a search if you haven't because it's wildly entertaining. There are babies who are scared of paper ripping but laugh hysterically afterwards or those who hate the sound coughing but follow up with a big grin. We had a similar situation going on in our house when my son was about three months old.
Turns out that our baby was both startled and delighted every time I sneezed. Mix that with the fact that we were going through a very bad allergy season, and we had some very funny times! It was so entertaining to see him go through those mix of emotions.
It happened like this. I would sneeze. I have a very funny, animated sneeze. I can't help it; it's just how it goes. My baby would then flail his arms, eyes wide, and become startled. But after that initial startle subsided, he'd smile and flash his drooly little grin. Sometimes we'd even get a giggle.