As it happens, I'm very familiar with 844, because when we left the Episcopal Church and went Straight Over to Rome, we consulted with our new rector regarding reception of the Eucharist before we were confirmed. He relied upon the precedent in the chancery of a couple who were ultra-high-church Piskies (as we were) who received in the Catholic Church in remote North Georgia because the local Episcopal parish was "low". Thus sec. 4 of Canon 844:
If there is a danger of death or if, in the judgement of the diocesan Bishop or of the Episcopal Conference, there is some other grave and pressing need, catholic ministers may lawfully administer these same sacraments to other christians not in full communion with the catholic Church, who cannot approach a minister of their own community and who spontaneously ask for them, provided that they demonstrate the catholic faith in respect of these sacraments and are properly disposed.Since we met these requirements vis a vis belief in the doctrines of the Church, including the Real Presence (I told you we were "high"), and our own ministers were unavailable because the Episcopalians had all gone stark raving mad, we were allowed to receive, after making good Confessions. But only after consultation with proper authority, not on our own.
Taking Communion is a significant and symbolic act. It states that you are "in communion" with the church or denomination in which you receive -- i.e. that you subscribe to all their beliefs and are a member of that community.
A Catholic cannot in good conscience "commune" with a church that is not in line with his beliefs, and the canons forbid his doing so. And a Lutheran, Presbyterian, Baptist, LCMS, whatever, should likewise refrain from communing with any church that does not adhere to his beliefs.
The Episcopalians, of course, don't believe in much of anything, so they let anybody come forward who feels like it. Reason # 4,729 why I am no longer an Episcopalian.
Bless you a thousand times!