I am worried about my friends mental health?

She is beginning to worry me with the things she does. She has lived in a shared house for about 5 years now but I still get regular phone calls saying she has a "crises" when she has just forgotten how to turn her heating/cooker off or has left the fridge door open. She obsesses over strange things and if incredibly forgetful. We often arrange to meet up and I will get a phone call about an hour after we made plans from her asking what I am doing today and should we meet up! Last week we got a bus together and she asked what number EVERY bus was that ped us and kept waving them down. She keeps sending me blank texts or texts that make no sense....I am pretty sure it isn't drugs I would of found it by now. any thoughts?