Haven't had a 503 yet, but page loading has definitely slowed again.
This reminds me of the annoying "memory stack" problems in earlier versions of Windows which required regular, fairly frequent reboots.
So, I googled.
I've been away from nuts and bolts too long to know if this is relevant, but it matches the symptoms:
Forbidden
"If you can keep your head while those around you are losing theirs, you can collect a lot of heads."