Do I have to sleep train again??

DS is almost 9 months. We sleep trained 5-6 months and he was happily falling asleep on his own for naps etc. The last 2 weeks all of a sudden it's back to he won't fall asleep unless he's held. We try leaving him but he just climbs the side of the cot and stands there crying for ages. Once he falls asleep we can't put him down either, or he wakes up screaming. He won't sleep in the car either so if we have to go out he's up all day and very cranky. We can put him down at night fine once he's fallen asleep being held, and he sleeps through. Just need to replace his dummy now and again if he can't find it himself through the night. Sleep training was so emotionally and physically exhausting, am I going to have to do it all over again again or will this pass with the 8 month sleep regression?