I bought a reasonably mature Zelkova indoor bonsa (1/2 metre high) from a reputed gardencentre in London mid September. It was in a poor state and heavily reduced due to a massive crack in the tray, thus not been watered for a while and lost 2/3 of its leaves. I couldn't leave it there to perish
so brought it home, knowing this would be a tricky problem since I don't know anything about bonsai trees. But I'm a resonably competent gardener, so was willing (indeed, the whole family)to give it tlc and see how we go. 
I looked through books so am fairly certain its a Zelkova carpinifolia, ie. Caucasian Elm. The leaves are chunkier and not as elongated & pointed as the other one. I fed it (1x) highly diluted Miraclegrow. Hubby mended the tray which sits inside a larger tray. The bonsai sits by a window in the S facing kitchen, so plenty of light. In the late afternoons when the sun was not so strong anymore I took it outside. Watered daily, ordinary tap water. It responded really well, within weeks it had masses of new leaves
We didn't have such a hot summer so I wasn't afraid of scorching etc. The temperature turned cool begin. of November but we didn't switch on our heating until mid November, so the house was fairly cold for a week or so. When the heating came on I regularly sprayed the tree as I do with other house plants. When we cook the tree gets removed to another room. And at night we put the tree away from the window.
About a week ago it started to lose leaves heavily, mostly green ones, a few yellow tinted, so clearly not an Autumn effect. Some leaves shriveled on the tree. By now it looks pretty much like when I bought it with only 1/4 of leaves still on.
Possibly I over watered it? I thought the shriveled dry leaves might be indication of drought but maybe I was wrong. I have bought bonsai liquid feed but haven't used it yet as I thought it's more for spring onwards. And I haven't used any other liquid feed, nor have I repotted it (wrong time of the year I presume) or trimmed it.
Do I allow it to dry out slightly? Do I wait for all the leaves to fall and then put it in the garage to overwinter it? (the garage faces NE, little light). Do I place it in a cooler room (eg.where I do my laundry) for the duration of winter? Do I keep it in the kitchen?
I think I understood that to put it outside is not an option as it hasn't become acclimatised yet. Having said that, I have a small spot by the house wall, on the terrace, facing south...So you see, kind people, that like the Macedonian lady, we are really keen to save it. Any advice is keenly appreciated.
Thanks, Patricia.
It's a Chinese Elm. Unfortunately can't send you a photograph just yet: my digital camera is "poorly" and my mobile phone is so old that the software isn't compatible with our new-ish computer. I'll get my daughter to use her phone, hopefully I can do this this evening. 
Once the pic is in my computer, how do I proceed?