Janice Combs was rushed to the hospital on Wednesday after she complained about discomfort in her chest ... according to sources close to Diddy. It's still unclear exactly what caused the pain, but we're told she's going to remain in the hospital for at least another day.

Our sources say Diddy was in Miami at the time, and at his mom's request, went to the hospital to be by her side. We're told Janice believes the pain is related to stress over her son's legal woes ... including the federal investigation and multiple civil lawsuits.

Janice lives in Miami, but at her own residence ... not with her son, who she famously raised on her own.

She has been seen spending time with him in Miami in the months since the federal raids on his homes. For several weeks, Diddy circled the wagons, and really only spent time with family members, like Janice and his kids.

We're told doctors are keeping her hospitalized another night for further testing and observation -- and Diddy is still there with her. As the source put it, "He's her comfort in this."

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