Bradycardia

The structural similarity to acetylcholine gives succinylcholine the potential to cause bradycardia, which is most often seen after a second dose.
Bradycardia may be prevented by preadministration of an anticholinergic agent, such as atropine or glycopyrrolate.

'Sux' pains

It is likely that the uncoordinated muscle fasciculations cause 'sux pains'. The jaw and neck are the areas most affected. They persist for a day or two and are most likely in women, particularly after day surgery.