To go backwards in Scripture is to incur God's wrath. To fall over backwards is a "sign" of that.
Two incidence where people fell over backwards. One (as you've already indicated) was Eli the priest. He fell over backwards when the ark of the covenant was captured.
The second were those who came to arrest Jesus.
Psalm 40
13 Be pleased, O Lord, to deliver me: O Lord, make haste to help me.
14 Let them be ashamed and confounded together that seek after my soul to destroy it; let them be driven backward and put to shame that wish me evil.
15 Let them be desolate for a reward of their shame that say unto me, Aha, aha.
This is a Messianic psalm and what he says here actually happened. Psalm 70 is the same language.
1 Make haste, o God, to deliver me; make haste to help me, O Lord.
2 Let them be ashamed and confounded that seek after my soul: let them be turned backward, and put to confusion, that desire my hurt.
3 Let them be turned back for a reward of their shame that say, Aha, aha.
This finds it's fulfillment in John
John 18
5 They answered him, Jesus of Nazareth. Jesus saith unto them, I am he. And Judas also, which betrayed him, stood with them.
6 As soon then as he had said unto them, I am he, they went backward, and fell to the ground.
7 Then asked he them again, Whom seek ye? And they said, Jesus of Nazareth.
Isaiah speaks of Israel's disobedience causing them to go backwards.
Isaiah 1
3 The ox knoweth his owner, and the ass his master's crib: but Israel doth not know, my people doth not consider.
4 Ah sinful nation, a people laden with iniquity, a seed of evildoers, children that are corrupters: they have forsaken the Lord, they have provoked the Holy One of Israel unto anger, they are gone away backward.
5 Why should ye be stricken any more? ye will revolt more and more: the whole head is sick, and the whole heart faint.
They received instruction that they did not heed.
Isaiah 28
12 To whom he said, This is the rest wherewith ye may cause the weary to rest; and this is the refreshing: yet they would not hear.
13 But the word of the Lord was unto them precept upon precept, precept upon precept; line upon line, line upon line; here a little, and there a little; that they might go, and fall backward, and be broken, and snared, and taken.
14 Wherefore hear the word of the Lord, ye scornful men, that rule this people which is in Jerusalem.
Isaiah 44
24 Thus saith the Lord, thy redeemer, and he that formed thee from the womb, I am the Lord that maketh all things; that stretcheth forth the heavens alone; that spreadeth abroad the earth by myself;
25 That frustrateth the tokens of the liars, and maketh diviners mad; that turneth wise men backward, and maketh their knowledge foolish;
26 That confirmeth the word of his servant, and performeth the counsel of his messengers; that saith to Jerusalem, Thou shalt be inhabited; and to the cities of Judah, Ye shall be built, and I will raise up the decayed places thereof:
Isaiah 59
13 In transgressing and lying against the Lord, and departing away from our God, speaking oppression and revolt, conceiving and uttering from the heart words of falsehood.
14 And judgment is turned away backward, and justice standeth afar off: for truth is fallen in the street, and equity cannot enter.
15 Yea, truth faileth; and he that departeth from evil maketh himself a prey: and the Lordsaw it, and it displeased him that there was no judgment.
Jeremiah 7
23 But this thing commanded I them, saying, Obey my voice, and I will be your God, and ye shall be my people: and walk ye in all the ways that I have commanded you, that it may be well unto you.
24 But they hearkened not, nor inclined their ear, but walked in the counsels and in the imagination of their evil heart, and went backward, and not forward.
25 Since the day that your fathers came forth out of the land of Egypt unto this day I have even sent unto you all my servants the prophets, daily rising up early and sending them:
Jeremiah 15
5 For who shall have pity upon thee, O Jerusalem? or who shall bemoan thee? or who shall go aside to ask how thou doest?
6 Thou hast forsaken me, saith the Lord, thou art gone backward: therefore will I stretch out my hand against thee, and destroy thee; I am weary with repenting.
7 And I will fan them with a fan in the gates of the land; I will bereave them of children, I will destroy my people since they return not from their ways.
Lamentations 1
7 Jerusalem remembered in the days of her affliction and of her miseries all her pleasant things that she had in the days of old, when her people fell into the hand of the enemy, and none did help her: the adversaries saw her, and did mock at her sabbaths.
8 Jerusalem hath grievously sinned; therefore she is removed: all that honoured her despise her, because they have seen her nakedness: yea, she sigheth, and turneth backward.
9 Her filthiness is in her skirts; she remembereth not her last end; therefore she came down wonderfully: she had no comforter. O Lord, behold my affliction: for the enemy hath magnified himself.
