DSM 5 already has this, called "Delusional Disorder":
A. Nonbizarre delusions (i.e., involving situations that occur in real life, such as being followed, poisoned, infected, loved at a distance, or deceived by spouse or lover, or having a disease) of at least 1 month’s duration.
B. Criterion A for schizophrenia has never been met. Note: Hallucinations, if present, are not prominent and are related to the delusion theme (e.g., the sensation of being infested with insects associated with delusions of infestation.
C. Apart from the impact of the delusion(s) or its ramifications, functioning is not markedly impaired and behavior is not obviously odd or bizarre.
A. Nonbizarre delusions (i.e., involving situations that occur in real life, such as being followed, poisoned, infected, loved at a distance, or deceived by spouse or lover, or having a disease) of at least 1 month’s duration.
B. Criterion A for schizophrenia has never been met. Note: Hallucinations, if present, are not prominent and are related to the delusion theme (e.g., the sensation of being infested with insects associated with delusions of infestation.
C. Apart from the impact of the delusion(s) or its ramifications, functioning is not markedly impaired and behavior is not obviously odd or bizarre.
[... etc ...]