Oh no!  Let's hope it's not serious!

Selena Gomez spent her Monday morning in an L.A. hospital emergency room ... but fear not, she's gonna be fine ... TMZ has learned. 

Sources close to the singer tell TMZ ... Selena has been suffering from a sore throat lately ... and this morning she thought she might have strep, so she decided seek immediate medical attention. 

We're told Selena had been suffering from symptoms yesterday ... and had to end a recording session early due to the pain. 

Also, Selena's step-father has been suffering from bronchitis, and she thinks she may have been exposed to something contagious. 

But sources tell TMZ ... so far, docs don't believe Selena has strep ... though the tests won't come back for a couple of days.

As TMZ reported, Selena went partying with (maybe) boyfriend Justin Bieber last night. No word on his throat is feeling this morning.

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