If you felt a tremor in Campbelltown or Appin late last night, it wasn't a dream.
The south-western Sydney suburbs experienced a tremor of magnitude 2.8 about 11.06pm just at or very close to the surface, Geoscience Australia's duty seismologist Eddie Leask said.
"I was siting on the lounge watching TV when I felt my body sway softly into the lounge," one smh.com.au reader said.
"At the same time I heard the walls and glass window areas creak quietly. That's when I realised my entire apartment was moving."
Every year, the south Sydney region experiences about two to three earthquakes between magnitude 1 and 2, Mr Leask said.
But while yesterday's quake was slightly higher than such tremors, Sydney is still considered a quiet earthquake zone compared with the rest of Australia and the rest of the world.
"Melbourne feels a lot more earthquakes down from the region to its south-east. Adelaide gets a lot of earthquakes and Perth is very close to a very large earthquake zone in Western Australia. So those towns get a lot," Mr Leask said.
"New South Wales is very big and so has a variety of regions but most of the earthquakes we get there are under the magnitude 6 range."
Some of the most recent larger quakes in the south Sydney region included a tremor of 5.5-magnitude in Picton on March 9, 1973, and a 4.7-magnitude quake on March 17, 1999, he said.
Australia's quakes are all intra-plate tremors, meant they stem from within a tectonic plate. While the earthquakes in our region are due to what happens on the edges of the plates, some of the stress generated by the plates' movement also gets released at weak points within plates, Mr Leask said.
"A lot of that stress is being released at the edges [and results] in the very large earthquakes that we see in New Zealand and Vanuatu and Tonga but some of the stress does translate into areas like Sydney or central NSW.
"It's like having a car accident. Not only does the bumper get crumpled - New Zealand - but also you might get some cracks across the windscreen due to the stresses happening through the entire car."
Mr Leask said that earthquakes now are recorded and analysed quickly.
In the 1960s and 1970s, "a lot of seismic stations through Australia allowed us to locate a lot more earthquakes then".
But in the past, such as in the late 1800s and early 1900s, most of the quakes were recorded through word-of-mouth "felt reports", he said.