I'm translating a post about psychology and having trouble with this sentence: 

>"I know when I'm sitting across from someone who's smiling brightly at me while simultaneously describing a significant loss or disappointment that I may have tripped over someone else who's hiding." 


The context is someone trying to hide their negative emotions. But I can't say for sure what exactly the author is meaning. I understand what is meant by *someone who's smiling brightly* but it's the latter part of the sentence which confuses me, i.e. ***while simultaneously describing a significant loss or disappointment that I may have tripped over someone else who's hiding***. 

Does the author mean while he/she is chatting with someone who's smiling happily, someone out there is having trouble and stuck in sadness but trying to hide these emotions?

Or he/she means, he/she talks about an unhappy one while chatting with the bright one?

Could you guys please clear up this sentence for me? Thanks so much.