Once in awhile I 'flatline' like that for a couple of days. . . I don't think it's anything to worry about. You had a nice temp shift, and I'd guess your hormones have just been superstable for a few days . . . just watch it for a while . . .
: Also possible the battery's dying, but I doubt it.
Ever seen "Rosencrantz & Guildenstern Are Dead"? Each time you flip a coin, there's a 50% chance it'll come up heads, even if it came up heads 100+ times before that. A flat line's a little unusual, but not outside the realm of normalcy.