Health and behavior are inextricably linked. And so changes in one of those categories often means that there's been some type of change in the other. If you know a person pretty well, and their behavior changes rapidly, or there are suddenly health issues that develop without an overt explanation, it might be time to either talk to them or do some investigating.
Depending on the signs and symptoms of the changes, you might want to have discussions about drug use, depression, body image, obsession with exercise, or even just issues with relationships. Everyone goes through some stress with those topics, but when it becomes severe, there are actions that should be done.
Signs of Drug Use
When a person starts using drugs, it can have an immediate and drastic effect on their behavior. Energy levels change, sleep cycles change, attitude changes, even friends change. And some people are better at hiding drug use than others, but the effects will still tend to bleed into other aspects of lives, and often in a negative manner. Most people don't become 'better' people when they use drugs, but only sobriety will bring this to light in the end.
Signs of Depression
Health and behavior are both impacted when a person begins to fall into depression as well. It's normal to feel sad in cycles, but especially when it comes to clinical or extended depression, it becomes difficult for the person going through things to see their way out of it, which is why they may indirectly rely on someone else's observations and interactions to help them get out of it. It never hurts to talk to someone who is exhibiting symptoms!
The Appearance of Body Image Issues
There are certain life events that can cause a person to reevaluate their body image, and often not in a positive way. A rude comment or situation where they’re feeling suddenly judged to be not worthy, and a person can spiral down into a place where poor self-esteem affects nearly every aspect of their life.
Sudden Obsession With Exercise
There's probably someone that you know in your life that suddenly became obsessed with exercise. There are tons of different causes of this, but it can be very curious seeing someone's basic temperament change because of a fixation on health - which, ironically, can be a sign of some other unhealthy aspect of their life becoming central in their mind.
Issues With Relationships
If a person is dependent on a relationship, a change in that relationship can quickly turn into an issue with health or behavior. Though it's normal to be interdependent with people you care about and love, too much dependency can lead to drastic changes in well-being if a partner is somehow removed from the equation. If you see someone going through this, try to help by talking them through it.