I am not familiar with a disorder called “dissociative stress disorder.” I do not believe that is a named disorder listed in the diagnostic and statistical manual (DSM) used by mental health professionals to diagnose psychiatric disorders.
What your brother may be experiencing is paranoia and he may be in the beginning stages of a psychotic break. Paranoia is usually a symptom of a named mental illness and is associated with bipolar disorder, schizophrenia, paranoid personality disorder or a general psychotic disorder not otherwise specified (NOS).
You also said that your brother has not slept very much in the past three weeks. His inability to sleep, along with the paranoia, is another possible indication that he may be on the verge of a psychotic break. It is not uncommon for an individual to experience insomnia preceding a psychotic episode. The fact that he is still able to function fairly well in other aspects of his life is encouraging but I am worried about how long he can sustain “normal” functioning in those areas of his life given the fact that he is barely sleeping.
I would strongly encourage you to try to persuade your brother to see a doctor immediately. If he is on the brink of a psychotic break, then it may be possible that it can be prevented if he begins taking an antipsychotic medication. It may be too late and the psychosis may be “too far along” to be stopped (if that is what’s occurring) but it is to his benefit to see a doctor immediately. He may not be on the edge of psychosis but only a doctor or mental health professional who met with him in person would be able to accurately assess your brother’s condition.
You said that he may not be willing to see a doctor. If this is the case, you can try alternative ways to convince him to go. For instance, you can try saying to him “I am worried about your lack of sleeping, perhaps you can see the doctor for something to help you sleep” and then, escort him to the doctor and inform the doctor about your brother’s behavior. The idea here is to not say “I think you may be paranoid and need help.” This would most likely result in him saying absolutely “no!” to a doctor’s appointment or any form of intervention.
Your goal should be to try and convince him to see a psychiatrist and if he refuses, then try to get him in to see any type of doctor, even if it is his primary care doctor. The primary care doctor should be able to recognize that your brother is experiencing unusual symptoms that signify a mental health issue. If you can, attend the doctor’s appointment with him or have another family member go with your brother so that you or the family member can inform the doctor about your brother’s abnormal behavior.
If you or your other family members cannot convince him to see a doctor, then be sure to monitor his condition. If he is on the verge of psychosis, then at some point his behavior may become more erratic and unstable. If this should occur, he may need to be hospitalized.
Please write back if you have any further questions.