Baby suddenly doesn't want to look at us?

My daughter (who is 3 months old) used to always look at us the entire time we fed her. She also used to spend a lot of time watching us do random things when we were in sight of her.

Recently she’s stopped doing all of this. I would be less worried if she was looking around at the environment around her – but she’s not (well, she does, but not when she’s doing this.). She just stares at a plain white wall for anywhere from 5 minutes to an hour, and fusses if we try to play with her or hold her or anything.

I know babies can be overstimulated, but she does this even when we haven’t done anything with her yet, like when she wakes up in the morning or after a nap.

When we feed her she normally just stares up at the ceiling. Sometimes her eyes get wider or she laughs at something, though there isn’t really anything there.

I don’t think she’s autistic, because when she does play with us she laughs and giggles and tries to talk to us – she is in no way introverted, except on these occasions where she stares at the wall or ceiling.

Is this normal behavior, for her to suddenly lose interest in her parents and prefer to stare at a plain wall or ceiling? Should I be worried?