Codependency Or Healthy Supportiveness

~A feeling of "shame" or "guilt" when you haven't actually done anything wrong
~when what you did was very trivial but the feeling you have is more like DREAD
~when you keep finding yourself dealing with serious anxiety over "normal life" things

These are flags that you are connected to one or more persons who have Control issues, and possibly personality disorder or other mental illness that manifests with Control toward other people.
What their 'issue' actually is would be for further observation, hopefully by a professional. But for a person who is connected with them, understanding that they are dealing with a person who has some kind of emotional or mental issue can be very helpful in understanding the situation in a more objective manner.
For instance, if one's brother had Bipolar disorder, but no one knew or understood what was going on, then other people in the family would likely either feel controlled by him, angry at him, or a more Narcissistic family might Scapegoat him or reject him completely.
A family (healthy family) who makes the effort to find out what his underlying issues really are, and who actually care about him, will be much better able to comprehend what's going on with him, and how to deal with it in a much better way for everyone. A competent professional counselor, therapist, or psychologist can be a key piece for a person who is dealing with a mental health issue, even if it's a temporary issue, but they can also be key for OTHERS* around a person who has a mental illness, whether it's severe or mild.
(Key word "competent")

*Narcissistic family members will not make this kind of effort to understand or help another family member, nor will a Narcissistic healthcare or mental healthcare provider; in both cases, they will try to place the entire "blame" and "burden" on the individual. So if this is the case (like if your brother seems to be bipolar, but no one else cares besides you), then you can find a decent counselor for yourself first, and if that person is competent, they can point you in the right direction as your brother's sibling and advocate.
Again, "competent" being the keyword. A Narcissistic counselor won't want to help you help your brother, and will probably treat you like you're being "codependent" or "Borderline" for doing the HEALTHY act of being supportive of a person you care about. They might even accuse you of "wanting to FIX people" (talk about projection!) Anyway if that turns out to be the case, they're not a good counselor anyway, so no loss when you stop going.