My hamster is acting strange?

i have 2 dwarf, roborovski hamsters and i have had them for around 18 months, so they are over 1 & a half years old they are female and have lived together for all their lives, i have one thats slightly larger than the other. the smallest of the 2 WAS the one that was the most active but now i never see it around the cage when i hold them the biggest one is still very active and trys to run away but the other one jus sits in my hand and closes its eyes, is there something that i can do, something i can feed it to boost up its energy? any help?? i have wagg hamster muesli which i feed them 20g of daily and i feed them 2 sources of fruit & veg 2-3 weekly, i have a fairly large cage with 2 levels i have a hide for them, tunnels, treats & gnawing sticks, i also treat them to a few dried mealworms twice a week is there anything else that i can do for them?