Joshua Jackson Hospitalized -- Bad Allergic Reaction

Joshua Jackson was rushed to the hospital Thursday night in Santa Monica ... after an intense allergic reaction ... Jackson's rep tells TMZ.


No word on what caused the reaction -- but he didn't seem too worried about the situation as he casually strolled out of the hospital soon after with his girlfriend Diane Kruger by his side.

TMZ spoke with Jackson's rep who told us, "Josh had an allergic reaction (not asthma attack)" ... adding, "[He] is perfectly fine."