"One random thing" - I think not I'm afraid. What has happened depends somewhat on the mail server you are connected to but I think I can guess.
I'm anticipating that your mail server runs both POP3 and IMAP as is common for most free and low cost mail services. At work, you are probably configured to use IMAP and at home you've managed to connect using POP3. It is possible that this is an Exchange server though which is configured to also support POP3 connections.
POP3 uses local mail stores, it was designed in the days when server storage was expensive, to keep costs down, the idea is that all users dragged their mail down to their PC. PC's were expensive too and mobile devices with email expensive and rare.
All has changed now and server storage is cheap. Many people also use multiple email capable machines and so it makes sense to keep mail on the server. Both IMAP and Exchange support this & it is a typical business/enterprise configuration as you get to control and back up the email centrally.
To fix using only Outlook. Create a local PST file on your home PC and drag everything into it. Now reconfigure your connection to use IMAP or Exchange as appropriate (check your work PC for the configuration or contact your IT support). Finally, drag all the emails from the PST file back. Presto, done. May take a while though if you've a lot of data. However, it should keep the unread marks, flags and so on.
Alternatively, you could follow the same process to create the local PST with the mail moved to it. Close the PST (very important), copy the PST to a memory stick and take it to work, copy the contents of the PST back to your main mail account there. Probably faster but relies on you being able to connect a USB memory stick at work.