Whenever a plant is shedding leaves for no readily apparent reason, it's time to take notice & review those things that COULD cause leaf loss. A reduction in light levels often causes some leaf loss, sometimes severe in particular trees - like Ficus. Tight roots and conditions of high moisture/low oxygen in the root zone also cause a drought response that manifests in the shedding of leaves. Plants can't think, they can only react; so when the root zone is flooded & compacted, plants can't easily take up water. The result is a plant dying of thirst in a sea of plenty because it can't effectively take up or move water - thus the drought response & raining leaves.

Al

Indeed, it is as Al says.
The Meyer lemon is particularly sensitive to changes in light and temperature. When you do move it outdoors, put it in partial shade to increasing sun over the course of two weeks.

Josh

Thanks for your help! I hope it doesn't drop any more leaves, new blossoms are opening up now and new buds are even forming. I guess this is a good sign? Also, I'd like to move it at some point out of the black growers pot and into terra cotta, when would you folks recommend I do this? It is draining well and I would guess it is not pot bound as it is in a large pot, but I like clay pots so much better than plastic. Even with drainage holes I just don't feel like they drain as they should. And thanks for the tips about moving outdoors!

If you're only potting up, you can do that any time, though it's best to do it when the plant is actively growing. Repotting is best done in the spring, but it can also be done right after a period of robust growth (citrus tends to add top growth in spurts followed by rest) spring through fall.

Al