Not sure about increased CPU load but the memory increase you described looks like Xen memory ballooning:
For example, if the Dynamic Minimum Memory was set at 512 MB and the Dynamic Maximum Memory was set at 1024 MB, this would give the VM a Dynamic Memory Range (DMR) of 512 - 1024 MB, within which it would operate. With DMC, XenServer guarantees at all times to assign each VM memory within its specified DMR.
When the host server’s memory is plentiful, all running VMs will receive their Dynamic Maximum Memory level; when the host’s memory is scarce, all running VMs will receive their Dynamic Minimum Memory level. If new VMs are required to start on “full” servers, running VMs have their memory “squeezed” to start new ones. The required extra memory is obtained by squeezing the existing running VMs proportionally within their pre-defined dynamic ranges.