If the mall seemed a little quieter this holiday season, it’s not just your imagination. Americans shopped online more than ever in 2015.

Cyber Monday, which takes place the Monday after Thanksgiving, became the largest online sales day ever last year, reaching more than $3 billion in sales. That’s a 12 percent increase over the previous year.

But even more impressive were the online sales in the days leading up to that Cyber Monday (Nov. 30). Online sales were up more than 25 percent over the four-day Thanksgiving weekend, as retailers shifted more bargains online and started those deals earlier.

As a result, brick-and-mortar stores took a hit, with at least a 10 percent decrease over the same period.

Not that there’s any reason to panic. Sales in those locations still topped $20 billion.

Throughout the November and December holiday shopping season, overall spending was up by about 8 percent over the same period in 2014, and online sales rose by 20 percent, according to a report from MasterCard.

This year marks perhaps the clearest indication yet that shopping patterns are shifting, and stores without strong web presence and the infrastructure to efficiently accommodate online sales will have to adapt quickly to keep up.

Presumably shoppers will no longer need to wait outside of stores in long lines before the sun comes up in order to take advantage of Black Friday sales.

That could be put a retail holiday “tradition” in jeopardy, though presumably online shoppers might be hunched over their keyboards, poised for early holiday action.

Interestingly, about a quarter of all online transactions were made over mobile devices, signaling the increasing importance of cell phones in retail sales.

Of course, physical stores still lead in overall consumer spending.

But for businesses large and small, consumer behavior is clearly changing.

The challenge will be keeping up.