Sounds to me like it has stretched. That happens mostly when there is a lack of light. How much lighting are you running? Plants stems get weak from lack of strength as well. Do you have a fan blowing on your plant to keep things cool? A fan blowing on the plant not only keeps things at a good temp., it also strengthens the stem for the weight in future.

The thing you can do now is get a small stick, and gently tie the plants stem to it to hold it up.