General slowness:
* Lethargic
* Drowsy
* Lagging
* Sluggish
* Torpid
* Unhurried
* Dawdling
* Lackadaisical
Lacking energy:
* Listless
* Enervated
* Exhausted
* Tired
* Wearied
Moving slowly:
* Creeping
* Crawling
* Dragging
* Meandering
For a person:
* Heavy
* Unresponsive
* Unenergetic
For a process:
* Stalling
* Bogged down
* Hampered
* Delayed
The best synonym will depend on the context of your sentence.