Hi, Clare. Is your sister's behavior UNUSUAL for her? Out of character?

Or is her most recent behavior part of a long pattern?

There are no pat answers here, but you have an opportunity to learn more by trying to engage your sister in a constructive dialogue. You might want to open with something like: "I know you have been under a lot of stress lately. Would you care to talk about it?"

Everyone is ALWAYS under stress, so you are very safe leading with this. You will come across as sympathetic rather than judgmental. Everyone needs someone to talk to, and you are offering her that opportunity. If your sister feels safe, she is likely to open up to you rather than be defensive.

You will probably find that whether there is a mental illness or not that some kind of personal stress was the trigger - family worries, financial worries, workplace worries, and so on. Even normal people fall apart under the strain. Those of us with a genetic vulnerabilty predictably go into an episode.

If she is undergoing an episode and is too far into it, rational conversation is impossible, and you will probably need to back off for the time being, and keep your fingers crossed. But active engagement is often a good way to bring a person down from an episode - at least to the point where they can take stock and figure out where to go from there.

If she does acknowledge stress, then you can start to ask leading questions. Work? Family? Don't be judgmental. Let her vent.Keep encouraging her to talk.

It's okay for someone to admit to stress. There's no stigma involved in stress. There's no blot on a person's character. As she opens up, you will have a lot more info to go on. Just stress? Possibly bipolar? Perhaps bipolar triggered by stress? Something else?

Keep in mind, your sister is likely to regard it as a breach of trust if you were to prematurely suggest she seek help. Her reaction: Here I am, I opened up to you, and you think I'm crazy.

This is actually a very rational thought, so you need to tread very carefully. But first you need to work on establishing a dialogue.

Good luck and please keep checking in ...