S.H.
If there is just water in the sippy cup... you can actually just leave the sippy cup in the crib/bed with him.
Or he may be going through a growth-spurt...2 years old they do this.
Or he may be having some molars coming in... this causes pain/teething.
Or is he possibly sick? When sick, kids get more clingy.
ALSO, at this age, they start to have "night-mares".. and perhaps "night-terrors". These are 2 different things, but are developmental based. Look it up online.
ALSO, kids at this age begin to get afraid of the dark.... night time fears. which is also normal and developmental based. So they want to be with/near the parent. They truly get scared... for real. Their imaginations are so active at this age.. and we can't just stop their minds or imaginations.
At this age, they go through a LOT of changes... developmentally. Its not easy for them either. And, they may still feel some separation-anxiety.... not only babies get this. Toddlers too. But it is manifested and expressed differently in an older child.
Maybe, try putting him on the floor, on a mattress.... in your room. If you don't want to co-sleep with him in your bed.
Can he talk or express to you, why he cries?
At this age... its not easy, for parent or child.
The poor fella... he sounds like maybe he is afraid of the dark or having night-mares. This does wake them. Both my kids, from that age, would start to have nightmares... or fear of the dark... and they'd wake... so I comforted them...
Also try making sure that before bed, he does calm things... not anything hyper or hyper TV or anything. Just quiet calm things... before bed. Give him a cup of milk before bed too... it calms children and even adults before sleep. Some kids also, really need to wind-down before bed, otherwise they have a hard time sleeping.
As he gets a bit older... he will get better about sleeping.
A good book is: "What To Expect: The Toddler Years." You can find it anywhere or on www.amazon.com
All the best,
Susan