Meyer lemon tree

Question

Brought plant inside, leaves are falling off is this what supposed to happen?

Answer 1

Yes, this will happen every year, unless you have a horticultural light of 200 watts or greater to keep it alive throughout the winter. Of course, no leaves for part of the year means no flowers, and ultimately no fruit, so if the fruit is what you are after, you will need to ensure that the tree has adequate light such as would be found outdoors in nature and cared for the same.
Temperature fluctuations can cause leaf drop too. The change from outside to inside may have shocked the plant. Also be sure you are watering till the water comes out the bottom of the pot. Here are more considerations:

https://www.gardeningknowhow.com/edible/fruits/citrus/leaves-falling-off-citrus-tree.htm
https://www.gardeningknowhow.com/edible/fruits/lemons/lemon-tree-leaf-drop.htm