Forcing me to change my password
I have been using iCloud perfectly well on my iPhone (9.1...I know, I'm updating it later this week) and MacBook Pro (10.10.5...also updating later this week). Since I'm updating later this week, I wanted to double-check that everything (mostly my photos) has been backed up properly, so I attempted to log in to my account on icloud.com. However, it won't let me log in. It seems to be forcing me to "Update your Apple ID" but I didn't ask to change my password, and I have not gotten this dialog box on either of my devices. My password is very secure (it's a phrase, with numbers, letters, and special characters).
I guess my question is...what happens if I change my password as it seems to be requesting? Will I need to re-log in to stuff? What will I need to re-log in to? I'm guessing: iTunes, iMessage, FaceTime, iCloud on my phone, App Store...what else? How will this affect my phone and laptop?
Thank you in advance for your help. I tend to have bad luck with technology, so I want to make sure I do things correctly. My mother was forced to change her iCloud password while purchasing a new iPhone at the Apple Store, and it messed up her account and prevented her from downloading her back-ups for weeks, so I would like to avoid this issue.
MacBook Pro, OS X Yosemite (10.10.5)