Ray J was admitted to a Las Vegas hospital last night with a severe case of pneumonia and heart pains, TMZ has learned.

A source close to the R&B singer tells TMZ ... Ray J remains in the hospital where he has received X-rays and an echocardiogram ... no word yet on the results.

This follows a serious case of pneumonia Ray J had four years ago during the height of the COVID-19 pandemic.

The 44-year-old "One Wish" singer was diagnosed with non-COVID pneumonia in 2021, and it was so bad, we were told Ray J thought he could die.

The bout put him on oxygen and temporarily required him to use an inhaler ... but he later recovered and soon after was breathing fine again.

Three weeks ago, Ray J announced from Tampa, Florida, that he was hitchhiking across the country. It's unclear if that's how he traveled to Vegas or if it had anything to do with his illness.