Ok, so, I've gotten master Conjuration and learned the thrall spells. Awesome fun. I was playing around with the "Dead Thrall" (perma-raise dead) spell, and now I have 4 active effects glued to me for what looks like 23,962 more game hours....

No biggie, except now everyone in Skyrim fears my deadly talents. I can't walk past anyone at all really without hearing them comment on my (absent) zombie pal (see topic title). Summoning new things does not help. I have no thralls following me anymore, just a stuck game effect.

From what I can tell the other three spells are safe, I've summoned a few elemental thralls, and no effects stuck relating to them.

Do the thralls take the place of a follower or can you have lydia and a thrall at the same time.

Thralls take the place of a summon. So, in theory, you can have yourself, a summon - two if you have the perk, a follower, and then THEY can have summons.. xD

Oh, and let's not forget your horse. Maybe a dog is also an additional 'slot'? Haven't gotten one yet. o.O