Vim Troubleshooting – Why is Vim Frozen?

I have two different machines (home and work) running Ubuntu 18.04. Last night vim froze at home. I was in insert mode and typing and went to save (esc :w) and nothing happened. The status bar still reads -- INSERT --, the cursor is still blinking where it was. I was stuck. I couldn't find a way out. I couldn't type (nothing happened when I type), I couldn't move around (the up and down arrows did nothing). It was stuck in insert mode with the cursor blinking where it was.

I was definitely multitasking and probably hit some other keys in there, but I don't know what keys. It was late, though, so I closed the terminal window and tried again (I was entering a git commit message). It happened again partway through my typing so I switched to git commit -m "don't need an editor for this" instead. And then I shut down my computer and stopped working.

I figured I was just tired, but then it happened to me today at work on a different laptop altogether. Again I was multitasking and can't swear I didn't type any bizarro key sequence but if I did it was accidental. And other tabs in the same terminal aren't frozen.

I'm used to getting trapped in visual mode in vim. That's a trick I've learned. But stuck in insert mode? Any ideas on what I might've done and how to get out of it?

Per a comment suggestion I tried looking at .viminfo but the only .viminfo I see is owned exclusively by root and only appears to show things I would have edited with sudo:

# Input Line History (newest to oldest):

# Debug Line History (newest to oldest):

# Registers:

# File marks:
'0  1  0  /etc/neomuttrc
|4,48,1,0,1531789956,"/etc/neomuttrc"
'1  1  66  /etc/apt/sources.list.d/signal-bionic.list
|4,49,1,66,1530816565,"/etc/apt/sources.list.d/signal-bionic.list"
'2  51  0  /etc/apt/sources.list
|4,50,51,0,1530816531,"/etc/apt/sources.list"

# Jumplist (newest first):
-'  1  0  /etc/neomuttrc
|4,39,1,0,1531789956,"/etc/neomuttrc"
-'  1  66  /etc/apt/sources.list.d/signal-bionic.list
|4,39,1,66,1530816565,"/etc/apt/sources.list.d/signal-bionic.list"
-'  1  66  /etc/apt/sources.list.d/signal-bionic.list
|4,39,1,66,1530816565,"/etc/apt/sources.list.d/signal-bionic.list"
-'  51  0  /etc/apt/sources.list
|4,39,51,0,1530816531,"/etc/apt/sources.list"
-'  51  0  /etc/apt/sources.list
|4,39,51,0,1530816531,"/etc/apt/sources.list"
-'  51  0  /etc/apt/sources.list
|4,39,51,0,1530816531,"/etc/apt/sources.list"
-'  51  0  /etc/apt/sources.list
|4,39,51,0,1530816531,"/etc/apt/sources.list"
-'  1  0  /etc/apt/sources.list
|4,39,1,0,1530816447,"/etc/apt/sources.list"
-'  1  0  /etc/apt/sources.list
|4,39,1,0,1530816447,"/etc/apt/sources.list"
-'  1  0  /etc/apt/sources.list
|4,39,1,0,1530816447,"/etc/apt/sources.list"
-'  1  0  /etc/apt/sources.list
|4,39,1,0,1530816447,"/etc/apt/sources.list"

# History of marks within files (newest to oldest):

> /etc/neomuttrc
    *   1531789952  0
    "   1   0

> /etc/apt/sources.list.d/signal-bionic.list
    *   1530816564  0
    "   1   66
    ^   1   67
    .   1   66
    +   1   66

> /etc/apt/sources.list
    *   1530816454  0
    "   51  0

It seems odd that I wouldn't have an unprivileged .viminfo but I did sudo udpatedb and locate .viminfo and still didn't surface more than the one root-owned file.