Conditions stacking reference?

[Remulus-5]

Hello!

I'm sure I've read somewhere that condtions stack with each other (Example : Dragon attacks 2 times => PC [4th+] fails once = shaken, PC fails twice = frighten) but I can't remember where. I've searched the DMG and DMG Faq but I didn't find it (obviously I didn't search well enough).
Can someone point out the page & book?

Thanks.

 

[Ferox4]

p. 83, DMG, in the intro to Condition Summary:

"If more than one condition effects a character, apply them all. If certain effects can't combine, apply the most severe effect."