It will grow more leaves where one has fallen. Just be patient. Mine always drops leaves in the winter.

A drop in temperature can cause this to happen. It also looks as if it needs repotting.

Hywel's right, that pot is way too small, so it needs potting up into a bigger one, but only 1 or 2 sizes bigger, not more. And it may need repotting in two years again into a bigger pot... a plant can only grow as well as its roots allow, and the roots of this one are probably completely cramped after 2 years...

This plant hates the cold. Keep it away from cold or cold drafts (above 50°F). It will drop it's leaves in a hurry. This is a succulent. It prefers dry arid conditions with bright indirect light. Water very occasionally, no fertilizer - maybe water every 2 weeks & be sure it has good drainage. Let it dry out between waterings. It hates wet roots. When you repot this plant, switch to a cactus mix. The potting mix you have it in now holds too much moisture & this plant hates wetness. It would love a loose sandy cactus mix. This plant thrives on neglect and is very forgiving. So, bright light, warm temps, loose sandy cactus mix, a splash of water every two weeks.

The corky, brown marks on the leaves are a sign of too much water. If you keep the dropped leaves in a dry place for a week or so the broken ends should callous over & you can push them a centimetre into a growing medium & eventually get new plants

Thank you that's all very helpful information.

After repotting,which looks as though it's needed,once it starts growing again,you could trim the lanky stems back to a lower leaf ,or joint,as it will readily start to grow from that point,and thicken up....The tops you take off will grow into new plants quite easily,if you pot them up..Definitely thrives on neglect,as my original one is going on for 30 years old..lives in an unheated Conservatory all winter..and outside in summer..in flower at the moment ,as is usual at this time of year..good luck,Andrea ...:o)

Thank you.