hamster sleeps a lot?

Question
i have just bought 2 hamster for 1 week and they're roborovski type. From the research from internet dwarf hamster should be alert and active. but my hamster is sleeping most of the time and they do not get up when i tap at their cage. All they do is eat and running around their cage for 5 minutes activity and they get back to sleep agian. Is there anything wrong with them?  

Answer
Dear Eline,
thank you for your question.
Maybe they are active only very late at night, some hamsters don't get up until one or two in the morning. If you suspect that they might be sick, please see a vet with them, I cannot give any advice on medical questions.
I'm sorry that I cannot be of more help to you
Jennifer