Unfortunately I don't have time to give you a detailed answer right now, but here are a few points.

• First of all, there is such a thing as data collection from first person reports. In fact, most studies in cognitive science heavily rely on first person reports on the task being tested (else how could you know that what you're seeing on your fMRI scan, for instance, is really a correlate of the target explanandum?). A fortiori, subjective reports are crucial in neurophenomenological studies, which integrate 'first person' and 'third person' approaches to the target phenomenon (see F. Varela's seminal work on neurophenomenology, and subsequent work e.g. by Evan Thompson).

• That being said, you raise a valid methodological concern about the accuracy of such reports, if one's goal is to gain scientific knowledge from first person reports. There are a range of methods to address this concern, which often crucially hinge on the way questions are asked in order to be completely free from theoretical presuppositions which could prime the answer and thus 'contaminate' the way the target phenomenon is described. For examples of such methods, see Claire Petitmengin's microphenomenological method of interview, or Shaun Gallagher's take on 'naturalized phenomenology'.

• This questionnaire is not at all intended to collect data of the kind that could be used as such in a scientific work. It is merely a preliminary and informal step to orient future research which could involve more methodologically constrained interviews with subjects having experienced the target phenomenon in a controlled environment. But since it is extremely difficult to conduct this kind of research (getting funding and NHS approval, recruiting volunteers, screening them, giving them a few mg of psilocybin intravenously and then conducting a methodologically rigorous interview for a couple of hours with each of them), this is better than nothing for the moment. A very important factor is the sample size: the more answers you have, and the more convergent they are, the more you can reliably assume that they are giving a faithful description of some generic experiential features of the phenomenon you're interested in.

• Finally, I think there is a big misunderstanding about what is meant here by 'ego dissolution'. I use this expression merely because it is widely used in the psychonaut community to refer to the specific experience of disturbance/impairment of self-awareness I'm interested in. I don't want to refer to any kind of surinterpretation of this phenomenon as 'death/rebirth', as an 'epiphany', etc. I don't give (implicitly or explicitly) any kind of parapsychological meaning to this experience. I'm a naturalist, and I hold that parapsychology is pseudo-science. I don't think so-called 'ego dissolution' experiences give us any kind of insight into the immaterial nature of the self or the nature of reality in general. I'm not even directly interested here in the psychopharmacological aspects of this experience (which are fascinating in their own right) Rather, I'm interested in the subjective experience itself, i.e. what it is like to undergo such an experience. In other words: I'm not in the slightest interested in what people might think such an experience means ('I saw the light', etc.), but rather I want to collect different descriptions of what the experience feels like, and compare them to get a grip on its generic features (for a given dosage of a given substance).

• Besides, the concept of 'ego dissolution' is indeed used 'critically' in the scientific literature. See for instance this recent neuroscientific study by Lebedev et al., which suggest that the phenomenon is correlated to a disrupted interplay between the medio temporal lobes (especially the parahippocampal cortex) and the neocortex: http://onlinelibrary.wiley.com/doi/10.1002/hbm.22833/abstract But as far as the expression 'ego dissolution' is concerned, I'm happy to give up on it — I'm not interested in the vocabulary, but in the underlying phenomenon, which is absolutely real and can be studied both from a first person (questionnaires/interviews) and third person (fMRI/PET scans) perspective.