One time (so far) startup issue

I have a 2012 Prius c with ~70k miles on it. Bought new, oil change every year at the longest (6800 mile road trip saw a change prior, midway, and a little bit after), haven't been in for a checkup past that in about 2 years.

I went to start it today and it came up, shifted into gear, and it died. Radio went, A/c was turned off (as in needed to turn it back on when everything eventually worked), dash lit up all lights. Check engine light came on when I tried to restart and it wouldn't come up. There was a slight hum coming from generally behind the steering wheel when I had car int he on position.

My first thought was battery, but the battery was more than half charged, according to the display, and i don't have a meter. Next thought was starter, which I didn't have the ability to fix myself then and there, obviously. I checked fuses, connections, all the basic easy to see things. Nothing. I finally remembered a trick my dad told me about years ago, just in case it was a simple switch or connector or something issue. I popped it into neutral, tried to start it. The dash lights flickered a little but nothing else happened. I popped it back into drive and it started up zero issue. I drove it around for a bit and the battery charges as normal. It has since started up normally twice since then.

What am I looking at here and how concerned in the short term do I need to be?

Thanks in advance

 

Thanks for the tips. I'll stop by the dealer monday and see if they have one and time to switch it. I had to scale down and just don't have the tools to do it until i have more space.