Bueno, en realidad es una construcción que se usa en el habla, lo correcto es "me olvidé de". Como función sintáctica es un Signo de Cuasirreflejo, es decir que depende del verbo "olvidarse", allí tienes el SE, pero como pronombre enclítico (enclítico=que se agrega detrás del verbo). Como clase de palabra o categoría gramatical, es un pronombre. Lo usamos en casos como: "Juan y María se peinan", en ese caso es un Objeto Directo recíproco, porque uno peina al otro. "Juan se peina", también es OD, porque el "se" sería como decir "Juan lo peina" (el OD se reconoce porque se lo reemplaza por "lo", "los", "la" o "las"), sólo que, como se lo hace a sí mismo, necesita el pronombre "se". Si dices "Juan se lo dio a María", el "se" refiere a María, así que es Objeto Indirecto (reemplazable por "le" o "les"), como decir "Juan le dio..." el "lo" reemplazaría a algún objeto, como no puedo decir "Juan le lo dio a María", "le-lo" no queda bien, se utiliza el "se". Es difícil de explicar, espero haber sido lo más clara posible. Saludos.

Hi Joe, as we are both English I will explain it to you in English as this will be easier both for me to explain to you and for you to understand. This happens with a few other verbs such as Acabarse = acabársele, perderse = perdérsele, olvidarse = olidársele, quemarse = quemársele. There are more/ I may be wrong but this is what I was told about these verbs. When you at the ''le'' or me, te, nos, os or les to the verb Example Rompérsele it shifts the blame from yourself or whoever else. Examples. He perdido las llaves. I have lost the keys = Its like its your fault. Se me han perdido las llaves. = Its like its not your fault, you did not do it on purpose, the blame is shifted to the keys. The keys have lost themselves. Se me olvidó contarte que = Its like its not your fault, you did not forget on purpose. Se nos ha quemado el pan. = The bread is burnt. OR the bread has burnt on us. Its the fault of the bread, we did not intentionally burn it. My explication my not be correct it is just the way that I intemperate it. I hope it helps and hope someone can correct me if I am wrong. The construction is. Se + me/te/le/nos/os/les + verb ha caído el vaso. etc.

Okay so that is a really tricky question that most Spanish students couldn't even answer. It is not something we think about when we talk and it is a matter of ''syntax''. In that case the verb is ''olvidarse'', which is not the same as ''olvidar''(there is a really really small difference in terms of meaning). By the way, as far as I know this is only for Spanish from Spain. I think the usage of this verbs may vary a little in some regions of South America. "olvidar" is transitive, so it needs a direct object: "olvidé las llaves" "olvidarse" is intransitive, and it needs the preposition "de" (Complemento de Régimen in Spanish). It is a ''verbo pronominal'', which means it always goes with a pronouns. Your case is a bit different because the use another trickier form with two pronouns. Here, the subject is actually the object you forget, and the indirect object is the person who forgets. This may be a little trickier, but it might help you. When you'd like to say ''a mi mismo'' or ''mutuamente'' you may change it for just ''se''. I hope I made it a bit more clear for you. I am sorry if I did not, it is a hard question and it's something we learn since we start speaking Spanish, so don't even realize what's going on but know how to use it. Good luck!

Hi, I'm also a Spanish learner and have the same problem with 'se', but here is how I understand it, hope it will be helpful to you. 'se', which you ask about, it can be seen as the preposition as the direct object, which means what is forgotten, the real content can be omitted. For example: se me olvida la fecha -- I forget the date--here 'se' refers to 'la fecha' se me olvidó por completo -- I forgot all about it;--here 'se' can be interpreted as 'it' se me olvidaba decirte que…I almost forgot to tell you that…--here 'se' can be interpreted as what 'que...' refers to.

Just to say thank you to everyone for your responses. I am very grateful to all for having taken the time to reply, it is much appreciated, and I think I understand the problem a lot better now. In summary, it seems that there are three different things going on (I think..): 1. The 'se' was referring to `that which had been forgotten' (i.e. his original intention to reply to the message), even though this fact had not been explicitly referenced as a direct object within the sentence. 2. As the word 'me' had already been used as the indirect object, (as is the case when we have two pronouns in succession) we have to change the one that comes first (the direct object) from 'lo' to 'se.' 3. As plsdeluno has pointed out, by phrasing the sentence in the way in which it has been, there has been a (subtle?) shift of blame by the speaker as he is saying it is not really his fault he forgot / he did not do it on purpose. This is what I have taken from this, but someone please correct me if I'm still wrong in my understanding. Many thanks!