At first I thought someone had serial downvoted me and the system was restoring my rep, but on closer inspection it looks like the opposite may have happen, I just don't understand why. :(
And yes, I've read the learn more link.
Your latest comment seems to answer this. Your physical proximity to another user (and their consistent attention to your questions and answers) seems to have triggered some sort of anti-sockpuppeting mechanism.
Per Shog9's post on the subject of sockpuppets
What you think is a sockpuppet could in fact be my good friend Nog Shine, who loves everything I write, copies my writing style, and uses my computer to vote and post stuff when I step away for coffee.
But in practice, there are patterns that are extremely unusual unless someone is using a second account. If it actually is a very enthusiastic friend, they should know better than to continue this behavior after being warned about it. Feel free to contact the SE team if you're unsure - we have a fair bit of experience in dealing with this sort of thing.
If you intend to continue operating two accounts from the same IP address, you'd be well advised to use the contact us link to explain your connection to the CMs and make it explicit that your actions are benign. They may (or may not) reverse the reversal but at the very least they'll offer some advice regarding the best way to prevent this from happening again.
As you can see, the majority comes from voting reversals where the system determined that there was voting abuse and reverse the upvotes. Serial voting can happen up or down.
In this case, it's because the system determined your accounts were sock puppets. While having a spouse or coworker upvote your posts is fine, you'll need to be more careful in that you're not upvoting/accepting their content in an unusual way (such as accidentally voting for them more often than others, which can happen easily when some in-person mentions a question you're both interested in). And the same is true of them.
The other account, Thirsty-Kitty, has very low activity. Because of this, their activity related to your account probably comprised too large of a portion of their actions, triggering the sock puppet reversals.