All the leaves have gone really limp and the stems have gone brown.
Any thoughts on what may have caused this and has my plant completely died?
Could be a couple of things.
a) cold draught at night could have caused it to go into winter mode early.. If the plant has been used to warmth and sudden cold draught for a period. Typically the leaves just fall off though.
b) Bacterial infection that has taken time - if the stems go squishy you know. This causes the plant to be fine one minute and the next minute everything just dies off as the bacteria destroy the stems etc. Overwatering can cause this.
c) struck by lightning given the thunderstorms last night near us!