When logging into single-player superflat worlds/ multiplayer servers, I start to experience major drops in fps. For the first 10-20 secs in singleplayer, I may have around 30 fps, but then it drops to 1 or 0 and stays in an unstable state, alternating between 1 and 0. Sometimes, I may get 18, 16 or 36 fps for a split second, but for probably 98% of the time it was 1 or 0.
I did not have this problem before, it only occurred to me when I started playing at aprox. 1:10 pm [South Ontario], on Aug 22 2017. Before this occurred, I had very little problems with my fps. It was usually in the 80-120 range. I did not edit, change or download anything in the past 5 days. Later in the day at around 7:00pm, I relogged back on to see if anything changed, sadly, no, and my low fps remained the same.
In default worlds, the problem doesn't seem to have such a profound effect. The fps there can range from 30(Mostly)-65(Rarely and only for a few seconds)

I did not check the amplified type worlds and customized worlds, as I did not have very pleasant pasts with them.

I believe that is all there is.