In Data Centers (DCs), an abundance of virtual machines (VMs) remain idle due to network services awaiting for incoming connections, or due to established-and-idling sessions. These VMs lead to wastage of RAM-the scarcest resource in DCs-as they lock their allocated memory. In this paper, we introduce SEaMLESS, a solution designed to (i) transform fully-fledged idle VMs into lightweight and resourceless virtual network functions (VNFs), then (ii) reduces the allocated memory to those idle VMs. By replacing idle VMs with VNFs, SEaMLESS provides fast VM restoration upon user activity detection, thereby introducing limited impact on the Quality of Experience (QoE). Our results show that SEaMLESS can consolidate hundreds of VMs as VNFs onto one single machine. SEaMLESS is thus able to release the majority of the memory allocated to idle VMs. This freed memory can then be reassigned to new VMs, or lead to massive consolidation, to enable a better utilization of DC resources.