Whereas interruptions is a very active subfield of research within HCI, as of today interruptions in immersive virtual reality (IVR) have received only little attention. We conducted a lab study (N=20) with a head mounted display (HMD) to understand the relationship between presence, workload and attention in IVR when measuring three virtual interruption designs. The answer to this question is interesting because prior research has revealed a positive effect on performance when providing intelligent interruptions, for example based on users' level of attention. Our work launches research on interruptibility in IVR by investigating (1) the relationship between attention, presence and workload, and the (2) methods for measuring them in IVR. Our analysis suggests that a trade-off between presence and attention is required when designing interruptions for IVR. Our findings are valuable for researchers and practitioners who want to collect data on attention, presence and workload in IVR to inform interruptibility.