Ghost player then server lag

I died in the nether and when I respawned in the overworld, a ghost of my player was at the spawn and wasn't moving. I continued as normal and collected some sand and then got huge server lag. I broke some sand and no drops came out; a few seconds later it reappeared and then broke, giving me the drops which took ages to pick up. I restarted the server hoping to get rid of the lag and when I went back on, my inventory was empty as if the other player had collected the items I dropped when I died and I didn't have anything. Everything that I changed while the ghost player was at the spawn was the same when I returned.