Put the summary of the bug you're having here

What I expected to happen was...:
When my character would go through the Netherworld portal, I would be able to move around without major lagging.

What actually happened was...:
When my character was in normal world, I was able to move around easily but when I went through the Nether Portal, my character lagged so much that it took a few minutes to be able to quit game. I tried a few times with the same results. In one of my games, I created the portal and went through. The game lagged and the portal disappeared. I killed the character in lava and tried again. The portal reappeared but majorly lags when I go through the portal. Sometimes it will return to almost normal but it takes several minutes (10-20 ish). Twice it has crashed.
There is nothing in the resource folder. I don't know how to change memory amount.
Steps to Reproduce:
1. Go through the portal